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RASITIC RHIZOCTONIAS IN AMERICA 



BY 



GEORGE LEO PELTIER 

A. B. University of Wisconsin, 1910 
M. A. Washington University, 1912 



THESIS 

Submitted in Partial Fulfilment of the Requirements for the 

Degree of 

DOCTOR OF PHILOSOPHY 

IN BOTANY 



IN 



THE GRADUATE SCHOOL 

OF THE 

UNIVERSITY OF ILLINOIS 
1915 



PARASITIC RHIZOCTONIAS IN AMERICA 



BY 



GEORGE LEO PELTIER 

A. B. University of Wisconsin, 1910 
M. A. Washington University, 1912 



THESIS 



Submitted in Partial Fulfilment of the Requirements for the 

Degree of 

DOCTOR OF PHILOSOPHY 

IN BOTANY 



IN 



THE GRADUATE SCHOOL 

OF THE 

UNIVERSITY OF ILLINOIS 



1915 






D. of D. 
JUL 81 1918 



UNIVERSITY OF ILLINOIS 

Agricultural Experiment Station 



BULLETIN No. 189 



PARASITIC RHIZOCTONIAS IN AMERICA 



By GEORGE L. PELTIER 




URBANA, ILLINOIS, JUNE, 1916 



Contents of Bulletin No. 189 

PAGE 

Introduction 283 

General Historical Account 283 

General Characters of Ehizoctonia 286 

Distribution of Ehizoctonia in the United States 292 

Distribution of Ehizoctonia in Canada 306 

Distribution of Ehizoctonia in South America and the West Indies 306 

Distribution of Ehizoctonia in Europe 306 

Distribution of Ehizoctonia in India and Australia 308 

Plan of Procedure 308 

Symptoms of Ehizoctonia Disease on Various Hosts 308 

Inoculation Experiments 337 

Discussion of Inoculation Experiments 358 

Growth on Media 364 

Measurement of Mycelial Cells 370 

Soil Survey of Ehizoctonia 372 

Parasitism of Ehizoctonia Solani Kiihn 375 

Summary 376 

Appendix 378 

Bildiography 386 




Fig, 1.— Carnation Stem Eot Caused by Ehizocto7iia Solani 



PARASITIC RHIZOCTONIAS IN AMERICA^ 

By GEORCIE L. PELTIEE, Associate in Floricultural Pathology 

INTRODUCTION 

One of the most serious and troublesome diseases which must be 
contended with by carnation growers in this country is the so-called 
"stem rot" due to the fungus Rhizoctonia. In 1911 a study of this 
disease was undertaken at the University of Illinois by Mr. H. W.| 
Anderson, at that time Assistant in Floricultural Pathology and now 
Professor of Botany in Wabash College. Since July, 1912, when Mr. 
Anderson left, a thoro investigation of those diseases of vegetable, 
field, and floricultural crops which are caused by Rhizoctonia has 
been conducted by the writer, the primary object being to determine 
whether infection is brought about by one or by more than one race or 
species of this fungus. The results of this phase of the work are pre- 
sented in the following pages. Extensive studies have also been made 
of stem rot, with a view to publishing at a later date. 

GENERAL HISTORICAL ACCOUNT 

The first description of Rhizoctonia was given by Duhamel,-'^-^ who in 
1728 found it causing a disease of saffron {Crocus sativus) in southern 
France. The diseased bulbs were thickly covered with a reddish vio- 
let network of hyphae which spread out into the surrounding soil, with 
knot-like swellings here and there in the mycelial network. Duhamel 
conceived these swellings (tubercules) to be the individual plants and 
the hyphse to be the roots, and named the fungus Tuheroides. 

Almost sixty years later (1785) another French investigator, Fou- 
geroux de Bondaroy,-^ mentioned that asparagus that was grown on 
land in which diseased saffron bulbs had been previously grown suf- 
fered from this same disease. Bulliard^^ in 1791 numbered it among 
the Truffles and named it Tuber parasiticum. Ten years afterward Per- 
soon^2 placed the fungus in the genus Sclerotium and called it Sclero- 
tium Crocorum. 

De Candolle,-"* who discovered a similar disease on lucerne, gave to 
the fungus the name RJiizoctonia. Later he distinguished three species, 
R. Crocorum, R. Medicaginis, and R. Mali. Nees"*^ in 1817 referred 



*The results presented in this bulletin formed part of a thesis submitted by 
the author to the Graduate School of the University of Illinois in partial fulfil- 
ment of the requirements for the degree of doctor of philosophy in botany, May, 
1915. Revised to date of issuance. 

283 



284 Bulletin No. 189 [June, 

to a fungus attacking crocus as Tlianatopliytmn Crocorum. This ap- 
pears, from his description and figures, to have been Rhizoctonia. A 
new species of Rhizoctonia was described in France by Duby^'' as RJii- 
zocionia Allii on Allium ascalonicum. In 1843 Leveille''"'* noted a simi- 
lar Rhizoctonia on Ruhia tinctorum, Solanum tuberosum, Pliaseolua, 
and Tulipa, without attempting to place it under any particular 
species. In 1851 the Tulasne brothers^^"^ classified all the forms, of 
Rhizoctonia as a single species, Rhizoctonia violncea, a classification 
which has been adopted by a number of writers. Rhizoctonia on cro- 
cus was reported in Germany in 1858 by Klihn.'''^ He also found this 
same fungus, which he identified as R. Medicaginis, on sugar beet. At 
the same time he described a new species of Rhizoctonia on potato, 
which he clearly distinguished from the above species and to which he 
gave the name R. Solani. 

In the United States, Rhizoctonia was first reported by Webber^^"^ 
in 1890 on the roots of alfalfa in Nebraska. He listed the fungus as 
Rhizoctonia Medicaginis DC. The first extended account of Rhizoc- 
tonia in the United States was given by Pammel,'^'^ who found it caus- 
ing a serious disease of beets in Iowa. Later, Atkinson^ observed 
Rhizoctonia causing damping-off of cotton seedlings, and following 
that, of a number of other kinds of seedlings. In 1901 Duggar and 
Stewart-^ ^ added a large number of hosts subject to Rhizoctonia attack. 
Many observations of other hosts and in new localities have since been 
made until at the present time Rhizoctonia has been found on one or 
more hosts in practically every state in this country. It has also been 
reported from Canada, the West Indies, South America, India, and 
Australia, so that it may be regarded as a truly cosmopolitan fungus. 

Duggar,' in an article published since this manuscript was com- 
pleted, brings out the fact that the violet root felt fungus, commonly 
known in Europe and the United States as R. violacea, should be re- 
ferred to as R. Crocorum (Pers.) DC. He states that unfortunately 
this name has priority over the more descriptive name R. violacea. 
Under R. Crocorum (Pers.) DC, Duggar lists the following pro- 
visional synonymy : 

Tuber parasiticum Bull. (1791) 
Sclerotium Crocorum Pers. (1801) 
BMzoctonia Crocorum DC. (1815) 
Bhisoctonia Medicaginis' DC. (1815) 
ThanatophyUtm Crocorum Nees (1816) 
Tuber Croci Duby (1830) 
BMzoctonia Bubice Dene. (1837) 
BMzoctonia Dauci Eabenh. (1859) 
BMzoctonia violacea Tul. (1862) 
BMzoctonia Asparagi Tckl. [non Fr.] (1869) 
HypocMius violaceus Eriks. (1913) 



"Duggar, B. M. : BMzoctonia. Crocorum (Pers.) DC. and B. Solani Kiihn 
{Corticium vagum B. & C.) with Notes on Other Species. Ann. Mo. Bot. Gard., 
2, 403-458, 9 figs., Sept., 1915. 



1916] Parasitic Ehizoctonias in America 285 

Under E. Solani Kiihn {Corticium vagum B. & C), the form com- 
monly found in this country and to a less extent in Europe, and the 
name generally used by American authors, Duggar gives the following 
synonymy : 

Bhizoctonia Betie Eidam [non Kiihn] (1887) 
Bhizoctonia NaycecB West. (1846) 
Bhizoctonia Bapw West. (1852) 
Hypochnus Solani Prill. & Del. (1S91) 

Duggar states further that with the evidence at hand a number of 
species of Rhizoctonia described from Europe may be excluded from 
the genus, while several species are doubtful. He adds that in all 
probability the six species described from America, listed in Saccardo, 
may also be excluded, altho a more critical study of material is needed. 

Many attempts have been made to connect the sterile fungus Rhi- 
zoctonia with a perfect stage. FuckeP^ in 1869 stated that the ascomy- 
cete ByssotJiesium circinans Fkl. (Leptospliaria circinans Sacc.) was 
the perfect form. However, beyond the association of these two forms 
on decaying stems of Mcdicago sativa, there were no signs of their con- 
nection. The same observation was also recorded by Prunet,^'' but again 
with no more conclusive proof than the presence of the two forms on 
the same plant. Massee''''' considered Rhizoctonia as representing the 
vegetative condition of Rosellinia, because of the fact that the struc- 
ture and color of the mycelium and the general habit of Rhizoctonia 
resembles that of the Fosellinia quercina Hartig and other destructive 
parasites belonging to that genus. He had no further evidence, how- 
ever, to support this supposition. 

During the summer of 1913, Cook,^** while examining tubers af- 
fected with Rhizoctonia, found a sclerotium that contained a mass of 
well-developed asci bearing spores. The mycelium of the sclerotium 
was characteristic of Rhizoctonia and the asci appeared to arise di- 
rectly from it ; this point, however, could not be determined with any 
degree of certainty. 

In 1891 Prillieux and Delacroix^^ described a basidiomycete, Hy- 
poclmus Sohnii, and altho at the time they did not associate it with 
Rhizoctonia, it has been accepted by a number of European writers in 
recent years as the perfect stage of R. Solani. 

In 1897 Frank^i reported EMzoctonia violacca as attacking grape- 
vines, and since a TJicleplwra was found associated with it, he pro- 
posed the name Tliclcpliora Rliizoctonirp. 

In 1903 Rolfs,''^ working with the Rhizoctonia disease of potatoes 
in Colorado, found constantly associated with this fungus a basidiomy- 
cete which Dr. E. A. Burt identified as Corticium vagum B. & C, var. 
Solani. He was aljle to trace the connection between the two forms, 
and completed his evidence when he obtained cultures of Rhizoctonia 
from single spores of the Corticium stage. 



286 



Bulletin No. 189 



[June, 



Eriksson^^ has described a new combination, Hypoclinus viola- 
ceus (Tul.) Eriks., which he believes is the perfect stage of RJiizoctonia 
violacea Tul. Plowever, beyond association on different plants in 
the same field, he appears to have no further evidence to show that 
the perfect stage which he found on a number of weeds is connected 
with R. violacea, found on a number of root crops. 

GENERAL CHARACTERS OF RHIZOCTONIA 

The morphological characters of Rliizoctonia Solani Kiihn varj^ 
with the age of the mycelium. The young hyphse branch at an acute 
angle from the parent hypha, subsequently lying parallel to it. A 
constriction is shown at the point of union, and a septum is generally 
laid down a short distance from this point. The threads are colorless 
and vacuolate. With age the hyphge lie more at a right angle with the 
main axis, showing less constriction. They deepen in color into a yel- 
lowish and then a rather deep brown, becoming more or less granular 
and empty. (Fig. 2.) Fusion of hyphse is very common and can be 
observed in any young culture of the fungus. It occurs either between 
hyphae of the same parent mycelium or between hyphae from separate 
colonies (Fig. 2). 

On many hosts a short tufted or bushy growth of the mycelium 
may occur with some strains^ This tufted growth is likewise present 




Fig. 2. — (1) Young Hyph^ of Bhisoctonia Solani; (2) Old, Brown, and Empty 
Hyph^ of Bhisoctonia Solani 



1916] Parasitic Ehizoctonias in America 287 

ill cultures of the strains that produce such growth on the host plants. 
T'he tufts are composed of brown hyphae, closely septate, constricted 
at. the septa, and often branching in an irregular manner. 

Sclerotia in cultures first appear as small, soft, white masses of 
hyphae. Later they become larger and turn dark and hard. Study of 
sclerotia at different ages shows that they are of uniform structure com- 
posed entirely of masses of irregular and barrel-shaped cells which 
break up into sections of one or several cells (Fig. 3). These shortened 
liyphal cells function as conidia and germinate readily under suitable 
conditions. Germination generally takes place by the protrusion of a 
tube thru the septum of a cell where it has broken away from an adja- 
cent cell. In some cases the hyphae of the germinating cells pass thru 
adjacent cells, which arc apparently empty. Occasionally these irreg- 
ular and barrel-shaped cells germinate equatorially instead of at the 
I'oles. After the germ tube has grown out some distance, it becomes 
narrowed near the germinating cell and a septum is laid down. The 
mycelium then develops in the usual manner (Fig. 4). 

The formation of sclerotia in nature is rather common on many 
hosts. The best known examples are those formed on the potato tuber. 
The size and shape of the sclerotia vary considerably. On potatoes 
they are small, about 1 to 5 millimeters, and are generally flat. On 
carnation plants they may reach a diameter of 5 to 8 millimeters. 
When the fungus is grown on soil in pure culture, they become 5 to 6 
centimeters in diameter (Fig. 5). 

The sporiferous stage of Rliizoctonia Solani was first observed in 
this country by Rolfs^"^ in 1903, on potato stems. It was described by 
Burt ^^ as Corticiuni vagum B. & C, var. Solani." In Europe this same 
fungus is generally known as HypocJinus Solani Prill. & Del." 

Altho the writer has observed Rliizoctonia Solani on seventy-five 
species of plants, including weeds and field, vegetable, ornamental, and 
floricultural crops, growing under diverse conditions and at different 
times of the year, for the past three seasons, it was not until the spring 
of 1915 that he found the Corticium stage. It was then observed in 
his home garden on bean, beet, radish, potato, parsnip, carrot, chard, 
spinach, pea, plantain, and pigweed. This stage was also found on 
winter vetch growing on newly plowed land, on carnation plants, and 
on a number of annual and perennial plants. In some cases patches of 
soil well protected from desiccation w^ere covered with the ashy gray 
mycelium of the perfect stage. 



"In a recent letter from Dr. Burt, he states : " I do not now believe that there 
is even a varietal diflference between CorticiMm vagum B. & C. and that on the 
potatoes; hence I shall drop var. Solani." 

•"In his monograph on the Thelephoracece, Burt" limits Hypochnus to resupi- 
nate species with colored, echinulate spores, while under Corticium he includes 
species always resupinate, which have colorless spores and lack cystidia. Accord- 
ing to Burt's classification, Uupochniis Solani Prill. & Del. becomes a synonym 
under Corticium vagum B. & G. 



288 



Bulletin No. 189 



[June, 




Fig. 3. — (1) Young, Barrkl-shaped Cells Which Compose the Sclerotia op 
Bhizoctonia Solani; (2) Older, Empty Cells prom the Sclerotia 




Fig. 4. — Germinating Sclerotial Cells op Rid-octonia Solani 



lUIll 



i'AKASlTK' KHIZOCTONIAS IN AmEKKA 



289 








# 














o 



Q 



290 Bulletin No. 189 [June, 

The presence of the Corticium stage seems to depend on climatic 
conditions. A cool season with an abundance of moisture is appar- 
ently essential for its development in the field. This stage is gener- 
ally found on plant tissues that are perfectly healthy ; it is in no way 
injurious to them. Some cases have been found where it had devel- 
oped on stems almost cut ofP by Rhizoctonia, but in no instance has 
the writer seen it form directly on a lesion or on injured tissue. (See 
Figs. 6 and 7.) 

The development of the Corticium stage may be described as fol- 
lows : The dark brown hyphse of the sterile stage gather, usually at the 
base of the plant, and from them arises an ashy gray mycelium, which 
forms a fine network around the stem. The development is usually 
faster where a little soil, thrown up by the rains, has formed a film 
around the stem. The extent of this fruiting layer varies, but it may 
proceed several centimeters up the stem. It is so lightly attached to 
the plant that it may easily be rubbed off. As it becomes old, it cracks 
and falls off. 

The outer hyph^ of the fruiting layer bear club-shaped basidia 
with four sterigmata and spores. Cystidia are lacking. The spores 
are colorless, oval to ovate, and have pointed bases. The usual spore 
measurement varies from 9 to 14 ju, by 6 to 8 fi. 

Cultures of Rhizoctonia from single spores of the Corticium stage 
have been obtained both by dilution methods and by the method used 
by Rolfs,^^ which consists in placing a stem covered with the fruiting 
stage over an open petri dish containing a nutrient agar, and allowing 
the spores to drop on the agar. 

Another fungus belonging to the genus Corticium, C. oclira- 
leucum (Noack) Burt (see footnote b, page 287), found in the United 
States by Stevens and HalPi'^-"^ on pomaceous fruits, has been care- 
fully examined by the writer. The mycelium of this species corre- 
sponds in many respects to that of R. Solayii and the development of 
the perfect stage is similar to the development of the Corticium stage 
of that species. It appears that these two species are very closely re- 
lated, but are entirely distinct forms. 

Duggar,* who has had an opportunity to study R. Crocorum 

(Pers.) DC. more at length, gives the following description of this 

species in his recent work : 

' ' The external, general hyphse are more or less different in form and appear- 
ance with age. The younger hyphas are usually dilutely violaceous with a pigment 
which may be decolorized l)y the application of acidulated water. The protoplasm 
is dense towards the tips of branches and vacuolated farther away. The hyphee 
are somewhat fiexuous, branched (sometimes closely), with the branches arising 
at right angles to the main hypha, and with a partition wall laid down at not 
over 10 fjL distant. "With age the hypha? become rigid, somewhat less in diameter, 
4-8 fi, the branching is distant, and these branches readily break off at the first 
partition wall. At the point of union the diameter is uniform with the main 

•See footnote, page 284. 



1916] 



Parasitic Rhizoctonias in America 



291 




Fig. b. — Green Tomato Showing the JSuPEKiiciAL Ashy Gray Mycelium of Cor- 
ticium vagum B. & C. Present at the Point Where the Tomato Touched 

the Soil 




Fig. 7. — Enlarged View of a Section of Pig. 6, Showing the Dark Strands op 
Hyph^ and Small, Spherical, Brownish Sclerotia of Ehhoctonia ^olani 
Kuhn with the Ashy Gray Network of Mycelium of Corticium vagum 

B. & C. (5x) 



292 • Bulletin No. 189 [June, 

hypha. The partition walls are distant, often 120-200 /x apart. The walls now 
possess the violet-brown pigment and in the Inmen little or no protoplasm is ob- 
servable. 

' * The internal mycelium is likewise branched, septate, often associated into 
loose strands, passing between the cells or traversing them. In the early stages 

of the disease, so far as reported, these internal hyphae are nearly colorless 

and are generally of less diameter than those constituting the external mat. 

" the hyphse constituting the external mantle may be uniformly dis- 
tributed, as is the case usually when the fungus attacks fleshy roots or tubers, or 
they may also form a number of aggregates having the appearance of loose or root- 
like strands. ' ' 

The infection cushions are distributed over infected roots. ' ' The external 
hyph^ are for the most part similar to those of the general mycelium, but there 
occur also branches in which the cells are short and swollen, sometimes resembling 

a short chain of spores The medullary portion of younger cushions is 

made up of finer, almost colorless hypha?, and it is this type which enters — strand- 
like — the cortical tissues of the root, destroying particularly the cambium and 
younger phloem regions. In the later stages of development it will be found that 
the cushions seem to extend considerably into the cortex, and more of the hypha3 
are colored. ' ' 

"The true sclerotia are flattened or rounded bodies varying in diameter from 
a few millimeters to several centimeters. When mature they are of a deep violet- 
brown and are thickly clothed with a persistent velvety felt, externally of the same 
color as the root-investing hyphaj, but darkening further in. Among the surface 
hypha? of the sclerotia as well as of the 'infection cushions' are found chains 
of enlarged cells quite distinct from the enlarged cells of E. Solani. The sclerotia, 
as noted previously, are always connected with the root felt by large hyphal 
strands. 

" a sclerotium consists) of fairly compact tissue made up of cells 

often considerably branched and sometimes curiously lobed. ' ' 

DISTRIBUTION OF RHIZOCTONIA IN THE UNITED STATES 

In Table 1 is presented a list of those species and sub-species 
which have been reported as being susceptible to R. Solani in the 
United States. It is obvious that as long as investigations on this dis- 
ease are continued, such a list cannot be regarded as complete or final. 
It may be noted that plants belonging to the families AmarantJiacece, 
Caryophyllacecv, Cruciferte, Leguminosa', SolanacecF, and Compositce 
are especially susceptible to this fungus. Under favorable conditions 
it can attack plants in these families at any stage, from seedlings or 
cuttings to older plants, when. grown either in the field or in the green- 
house. About fifty important families of flowering plants are repre- 
sented, several gj^mnosperms, and Equisetum, one of the Pterido- 
phytes. The list includes a number of monocotyledons, which for- 
merly were reported as being not susceptible to Rhizoetonia. Among 
the dicotyledons are many annuals and perennials, including herbs 
and woody plants, as well as most of the greenhouse and garden 
plants, field crops, and weeds. 

R. Crocorum, as will be seen in Table la, has been reported so far 
in this country from only a few scattered states. It is probable that 
as investigations continue this fungus will be found in many other 
localities. 



lf}W] 



Parasitic Ehizoctonias in America 



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306 Bulletin No. 189 [June, 

DISTRIBUTION OF RHIZOCTONIA IN CANADA 

In a letter to the writer, Dr. II. T. Giissow of the Central Experi- 
mental Farm, Ottawa, Canada, stated that he had observed Rlii- 
zoctonia Solani on potato, pea, sweet pea, and aster. That the stem 
rot of carnation also occurs in Canada is shown in a paper read by 
John Morgan of Hamilton, Ontario, before the Canadian Ilortical- 
tural Association at Guelph, in August, 1906! 

DISTRIBUTION OF RHIZOCTONIA IN SOUTH AMERICA AND 
THE WEST INDIES 

The following list of plants reported as susceptible to R. Solani 
in South America and the West Indies, with character of injury, has 
been compiled from Cook's^^ Diseases of Tropical Plants: 

Bean X)amping-oflf, dry rot of stem, and pod rot 

Beet Eoot disease 

Cotton Damping-oflf and sore shin 

Cucumber Daniping-off 

Lettuce Damping-off 

Melon Damping-off 

Nursery stock Damping-off 

Pea Root and stem rot 

Potato On stem and tubers 

Seedlings Damping-off 

Sweet potato Root rot 

Tobacco Seed-bed rot 

Tomato Rosette and fruit rot 

DISTRIBUTION OF RHIZOCTONIA IN EUROPE 

Despite the wide distribution of Rhizoctonia in Europe, the nomen- 
clature of the species is in a very confused state. Some writers under- 
stand RMzoctonia Crocorum (Pers.) DC. to include several species, 
while others treat it as a separate species including forms with a rich 
violet mycelium. This uncertainty extends to the other common species 
of Rhizoctonia, so that the European literature on the subject offers 
many difficulties. Another fact which adds to the confusion is that 
both RMzoctonia Solani and RJiizoctonia Crocorum attack potato 
stems and tubers, and while the symptoms caused by the two fungi can 
be easily distinguished from one another in the field, it is another mat- 
ter to differentiate between them in literature. 

A partial list of the hosts in Europe which are attacked by Rhizoc- 
tonia is given below to show the extent of the distribution of this fun- 
gus. Only the more important references are mentioned. 

Austria Hungary. — Rhizoctonia was first reported in Austria Hun- 
gary in 1875 on potato. Later R. Crocorum was found on sugar beet, 
potato and lucerne, and R. Solani (Corticium vagum), on potato. 



1916] Parasitic Riiizoctonias in America 307 

Belgium.- — R. Crocorum has been observed in Belgium on sugai' 
beet, potato, and asparagus. 

Denmark. — E. Rostrup,'^''"^^ during the years 1884-1905, reported 
Rhizoetonia in Denmark on a large number of hosts, including many 
weeds and the roots of several species of forest trees. Among the 
cultivated crops mentioned are carrot, clover, lucerne, kohl-rabi, beet, 
turnip, sugar beet, and potato. Both R. Solani and R. Crocorum 
were observed on the potato. In 1892 Rostrup described a new species 
from turnip, which he called RJiizoctonia fusca and which differed 
only in one or two essential characters from R. Crocorum, also found 
on turnip. 

England. — Rhizoetonia was first reported in England on mangel 
in 1901, and on potato in 1904. The next year Giissow,'*^ in an ex- 
tended account of this disease, stated that it was due to R. Solayii. 
Salmon,i*^i in working on a disease of seakale due to R. Crocorum, 
found that it was also able to attack salsify, parsnip, carrot, parsley, 
lettuce, and potato. 

Finland. — Reuter'^i has studied a Rhizoetonia in Finland which 
causes a root rot of rye. R. Crocorum has been found on beet. 

i'^rawce.— Between the discovery of R. Crocorum in France in 
1728, on crocus, and 1851, a number of hosts, including asparagus, 
bean, clover, Citrus, Coronilla, grape, onion, Ruhia, Samhucus, and 
tulip, were reported. 

Germany. — In 1858 Kiihn*^'^ found R. Crocorum on sugar beet in 
Germany and described the species R. Solani on potato and carrot. 

Eriksson^^ states that in Germany in 1893 R. Crocorum appeared 
on sugar beet in several places; on lucerne, in 55 localities on plants 
1 to 5 years old ; on potato, in 11 localities ; on asparagus, in 3 locali- 
ties ; on hop, in 1 locality ; and also on a few weeds, such as Taraxacum 
officinale, Convolvulus arven.sis, etc. ; and that in 1894 it was observed 
on lucerne, in 77 localities; on potato, in 11 localities; and on red 
(lover, in 8 localities. The species R. Solani {Corticium vagum) and 
/)'. Strohi Scholtz on white pine, have been; recorded. 

Holland. — Dr. Johanna Westerdijk reports both R. Crocorum and 
R. Solani as being very abundant on potato in Holland. 

Ireland. — PetJiyhridge *^"^^ has shown that both R. Crocorum and 
R. Solani are present on potato in Ireland. 

Italy. — R. Crocorum has been reported at various times as present 
on alfalfa, sugar beet, clover, asparagus, carrot, parsley, chard, the 
roots of grape, and many weeds in Ital3^ RJiizoctonia destruens Tassi 
occurs on the roots of DelpJiinium. 

Portugal. — The Rhizoetonia attacking sugar beet has been reported 
from two localities in Portugal. 

Russia. — R. Solani was reported on potato in Russia in 1899, 



308 Bulletin No. 189 [June, 

Sweden. — Eriksson"^'^ ""^ observed a disease of carrot and beet in 
1898 in Sweden, caused by R. Crocorum. He was able to inoculate 
this fungus on garden and sugar beet, alfalfa, potato, and many weeds 
— Stellaria media, Myostis arvensis, Galeopsis, TitraJiit, Erysimum 
clieirantJioides, TJrtica dioica, and SoncJius sp. In addition to these 
hosts Eriksson has reported R. Solani {Corticiiim lutgiim) on potato 
and R. Crocorum on turnip and kohl-rabi. 

DISTRIBUTION OF RHIZOCTONIA IN INDIA AND 
AUSTRALIA 

Shaw,^^^ working on the morphology and parasitism of Rhizoctonia 
in India, reported RJiizoctonia Solani on peanut {AracJiis lujpogoea), 
cowpea (Vigna catjang), jute {CorcJiorus capsidaris), DolicJios Lab- 
ial), Tricliosantlies cucumernia, soybean {Glycine soja), mulberry 
{Morns alha), sesame, melon roots, cotton, roots of Agave rigida, and 
potato. 

In Australia, McAlpine''"^ found R. Solani very widely distributed 
on potato, 

PLAN OF PROCEDURE 

The main object of the present research was to determine whether 
of the culturable forms of Rhizoctonia one or more than one race or 
species is present in this country. The work was taken up from the 
following standpoints : 

1. Symptoms of Khizoetonia disease on various hosts 

2. Inoculation experiments 

3. Growth on media 

4. Measurement of mycelial cells 

5. Soil survey 

SYMPTOMS OF RHIZOCTONIA DISEASE ON VARIOUS 

HOSTS 

Following are presented the observations of the writer concerning 
the nature of the diseases caused by Rhizoctonia on the various hosts, 
together with the principal facts which appear in literature regarding 
Rhizoctonia on the more important crop plants in this country. 

Alfalfa, Medicago sativa 

On March 17, 1914, the attention of the author was called to the 
damping-off of young alfalfa seedlings in the agronomy greenhouse 
of the Station. Microscopic examination and pure cultures showed it 
to be due to Rhizoctonia. The seeds had been sown in rows in pure 
quartz sand and kept well moistened. The young seedlings, on ger- 
mination, were somewhat crowded, so that the conditions were very 



1916] Parasitic Kiiizoctonias in America 3U9 

favorable for damping-off. The fungus could be seen extending in all 
directions over the surface of the sand. 

The fungus found on the diseased alfalfa seedlings was compared 
with a fungus obtained from mature alfalfa plants sent from Iowa. 
Altho the mycelium of the two forms was characteristic of Rhizoctonia, 
it differed in many respects, particularly in the color of the hyphse. 
The form on the mature plants Avas undoubtedly Rhizoctonia Cro- 
(ormn, while that on the seedlings was the common Rliizoctonia Solaiii. 

Rhizoctonia was first reported on the roots of alfalfa from Nebraska 
in 1890, by Webber,!^''' q^<^ RJiizoctonia Medicaginis DC. This fungus 
was next mentioned on alfalfa as Rliizoctonia violacea, by Heald,^'^ 
who found it causing a root rot in a single locality in Nebraska in 
1906. In 1908 it was reported by Freeman,^^ under the name Rliizoc- 
tonia violacea, as spreading rapidly in the alfalfa fields in Kansas. 
Freeman described the disease as beginning in different parts of the 
field where at first a single plant dies. From these centers of infec- 
tion the fungus grows in all directions thru the soil, killing the plants 
as it proceeds. Thus circles of steadily increasing radii are formed, at 
the edges of which plants in all stages of the disease are found. The 
great majority of the plants within the affected areas die, while those 
which survive are not vigorous and always lose their main tap roots. 

The first external sign of the disease is a yellov/ing of the plant, 
which soon after wilts and dies. The roots of a dead or dying plant 
are found to be covered with a violet or brownish red mat of mycelial 
strands, or hyphee. In a few cases the tap root is completely rotted. 
In less severely affected plants, the cortex of the roots slips off easily 
when the plants are lifted from the soil, leaving only the central woody 
cylinder. This condition is due to the fungous threads which grow 
thru the cortex as far as the cambium layer, which they kill. The 
fungus forms sclerotia, which may live in the soil for several years. 

Stewart^ "*^ in 1908 mentioned a root rot and damping-off of alfalfa 
in the field in New York. His description of the disease; agrees in 
some respects with the one given by Freeman. Later he also noticed 
the damping-off of alfalfa seedlings in the greenhouse. He was not 
certain that Rliizoctonia Crocorum was present in New York, and was 
of the opinion that the fungus causing the damping-off of seedlings 
in the greenhouse was different from the one found in the field. 

Hcald,^'^ in a later article (1911), described more fully the disease 
occurring in Nebraska. At that time he regarded the fungus as iden- 
tical with Rliizoctonia Medicaginis DC. of Europe. 

From the above accounts it is certain that there are two species of 
Rhizoctonia in this country able to attack alfalfa — R. Solani, widely 
distributed, causing only a damping-off of seedlings, and R. Crocorum, 
with a limited distribution, attacking as a rule only mature plants 
in the field. At present this latter species has been reported on alfalfa 
from Nebraska, Kansas, Iowa, and Virginia. 



310 Bulletin No. 189 [J^ine, 

Alternanthera, Telantkera sp. 

In the fall of 1912 cuttings from alternanthera, coleus, and salvia 
plants which had been placed in the same bench were found to be 
damping-off. A microscopic observation and pure cultures from dis- 
eased cuttings showed that Rliizoctonia Solani was the causal organism. 
Later the fungus was found on alternanthera plants in the field, but 
apparently it caused no injury there. 

Alternanthera plants grow low and bushy, and thruout the sum- 
mer, no matter how dry the season, the soil underneath is usually 
moist. On close examination of the tangled mass of branches, strands 
of a fungus, which were later found to be made up of bundles of 
hyphse, could be seen spreading in all directions. At first glance the 
masses of mycelium looked very much like old spider webs. A number 
of different varieties of alternanthera were examined, and all were 
found to have the characteristic brown strands ramifying upon the 
surface of the whole under side of the plant. The reddish varieties 
seemed to have more of the fungous strands than did the green and 
variegated plants. Cultures from the brown strands in every case 
yielded pure cultures of Rhizoctonia which corresponded morphologi- 
cally and physiologically to the Ehizoctonia obtained from the cut- 
tings. 

Whether the fungus was at any time parasitic on the plants in the 
field was questionable. However, cuttings made from them still con- 
tained pieces of mycelium, and when placed in sand in the greenhouse, 
the fungus did parasitize not only the alternanthera cuttings but others 
as well. 

The belief that Rhizoctonia is present on the branches of the alter- 
nanthera plant thruout the year was corroborated in 1913 and again 
in the fall of 1914, when the cuttings made from plants in the field 
began to damp off in the cutting bench. Repeated observations showed 
that the fungus was present on the plants in the field, notwithstanding 
the fact that they had been planted in new soil. Old plants brought 
in from the field were cut close to the roots and planted in flats in the 
greenhouse. These sprouted and developed new shoots, from which 
cuttings were made. Many weeds came up in the flats during the win- 
ter, and in March both the cuttings and the weeds became infected 
with Rhizoctonia. It seems, therefore, that the fungus is present on 
alternanthera at all times of the year, tho the only injury it causes is 
damping-off of cuttings in the greenhouse. 

Alyssum, Sweet, Alyssum odoratum 

During June, 1914, when the bedding and decorative plants were 
being set out from the floricultural greenhouses of the Station, about 



1916] Parasitic Ehizoctonias in America 311 

twenty-five plants of sweet alyssum growing in two and one-half inch 
pots were found to be diseased. The plants were tall and had fallen 
over from their own weight, so that they formed a mat over the pots. 
On close examination the soil and plants were found to be covered 
with the strands of brown mycelium which are characteristic of R. 
Solani. A number of these plants died, while on the stems of others 
the fungus formed small lesions near the surface of the soil. The fun- 
gus continued- to grow on diseased plants placed in the field, and 
killed a few more of them. 

Amaranthus 

Specimens of Rhizoctonia on Amarantlius retro flexus were received 
from Mr. W. H. Burkholder of Cornell University. The mycelium of 
the Corticium stage could 1)e easily recognized on the stems, while the 
Rhizoctonia stage was plentiful on the lower part of the plant. A cul- 
ture Avas obtained from scrapings made from the mycelium of the Cor- 
ticium stage. Several spores were found and one basidium showing 
the four sterigmata was observed. 

Duggar and Stewart^- reported the occurrence of Rhizoctonia on 
Amarantlius retroflexus (pigweed) and A. alhus (tumble-weed) in 
New York in 1901. Several years later Rolfs^^ found the perfect 
stage, Corticium vagum, in Florida on A. retroflcxus and A. sjnnosus. 

Asparagus, Ornamental, Asparagus sprcngeri 

Duggar and Stewart"- observed the effects of Rhizoctonia on a 
number of plants of ornamental asparagus. They found that the 
])lants were killed and that many of the leaves were bound to each 
other by the brown threads of the Rhizoctonia hyphae. 

Aster, China, Callisteplms lioricnsis 

Damping-off of aster seedlings was noticed in flats in the floricul- 
tural greenhouses in the spring of 1913 and again in 1914. The dis- 
ease first appeared as a small, brown spot on one side of the seedling 
at the surface of the soil. This lesion increased in size until the seed- 
ling fell over. After a number of seedlings were prostrated, the fun- 
gus spread over them, and in time a mat of mycelium covered the sur- 
face of the soil. 

In May, 1914, a iiumbci" of aster plants, four to five inches high, 
were planted in old soil in which several varieties of carnation plants 
had been growing during the winter. There had been more or less 
stem rot among these plants all the season. After a month, when the 
aster plants were about 6 inches high, they began djnng off and con- 
tinued to die until they were from 9 to 12 inches high and ready to 



312 



Bulletin No. 189 



J line. 



bud. Other aster plants set in new soil at the same time that these 
were transplanted developed normally with no stem rot whatever. 

Table 2. — Mortality of Different Varieties of Aster Grown in Old Carna- 
tion Soil Infected with Bhizoctonia Solani 



Variety 

Queen of the Market .... 

Lavender 

Azure Blue 

Purple 

Pure White 

Shell Pink 

Eose Pink 

Deep Eose 

Crimson 



Number of 


Total 


Total 


plants 


dead 


healthy 


50 


1 


49 


50 


1 


49 


50 


4 


46 


50 


7 


43 


100 


13 


87 


50 


2 


48 


50 





50 


50 





50 


50 


1 


49 



As can be seen from Table 2, plants from all but two of the varie- 
ties died in the bench. The varieties Azure Blue, Purple, and Pure 
"White were planted where most of the stem rot on the carnations oc- 
curred ; hence the higher number of diseased plants in those varieties 
is due to location rather than to varietal susceptibility to Rhizoctonia. 

Obviously the Rhizoctonia causing carnation stem rot was in this 
case able to attack healthy aster plants. The stem rot of these plants 
was typical and very similar to the rot of carnations. The first sign 
of the disease was a yellowing and drooping of the foliage, followed, 
sooner or later, depending on weather conditions, by a sudden wilt- 
ing of the whole plant. When the plant was pulled, the bark of the 
stem near the surface of the soil would slough ofP, leaving only the dis- 
colored woody tissues. 

A stem rot of aster due to Rhizoctonia has been reported only once 
before in this country. Duggar and Stewart'^ ^ j^ 1901 found the my- 
celium in the tissues of aster and later isolated a pure culture from 
them. They observed the disease in a number of localities in New 
York during that summer. 



Bean, PJiaseolus vulgaris 

The damping-off of young bean seedlings by R. Solani, which 
has been observed in the greenhouse and in the field, is characterized 
by the production of small lesions at the surface of the ground either 
on one side of the stem or girdling it, followed by the falling over and 
death of the seedling. 

When the fungus attacks older bean plants, lesions of various 
sizes are produced just below the surface of the ground, at the surface, 
or one or two inches above it. In some plants these discolored spots 
can be found on the larger roots also. The lesions, as a rule, have a 



1916] 



Parasitic Ehizoctonias in America 



313 




Fig. 8. — Stems of Mature Bean Plants Which had been Placed in a Bench 

Infected with llhirjoeionia Solani Originally Obtained from 

Carnation Plants 



reddish brown band with a lighter colored, sunken area, and extend 
thru the cortical layer into the woody tissues. As on the young seed- 
lings, the spots are usually localized on one side of the stem, but in 
some cases one lesion may girdle the plant. These lesions weaken the 
stem and cause it to break off easily. 

The first account of Rhizoctonia causing a disease of bean was given 
by Atkinson.* He reported that during the winter of 1894-95 it 
caused damping-oft' of bean seedlings and attacked plants that were 
from 6 to 10 inches high. He referred to this form as "the sterile 
fungus," and stated that its most characteristic peculiarity was the 
mode of branching. 

In 1901 Duggar and Stewart^ ^ reported this fungus, from New 
York, as the cause of a stem-rot disease of red kidney beans in the field 
and of a damping-off among seedling beans in the greenhouse. 



314 Bulletin No. 189 \June, 

In 190-1 lledgcock"'" reported as follows: 

"The bean crop in the vicinity of St. Louis was severely injured by a Khi- 
zoetonia which attacked the stems and large roots of the plant and also produced 
brown sunken areas on the surface of the pods, penetrating the latter and discolor- 
ing the seeds. An examination of a number of seeds whose surface was discolored, 
disclosed the fact that the mycelium of the fungus had established itself in the 
second coat and in many instances had formed minute sclerotia there without rot- 
ting the seed or even penetrating the cotyledons. The presence of the fungus did 
not prevent the germination of the seed. ' ' 

Fulton^ ^ in 1908 showed that Rhizoctonia from infected pods 
caused damping-off of seedling beans and of month-old plants. 

A serious outbreak of the stem rot of beans was reported from New 
York by Barras^ in 1910. He found that in some fields as many as 
30 percent of the plants w^ere infected. In the same fields during the 
following season it caused the death of at least 5 to 6 percent of the 
seedlings ; later in the season, after a rainy spell, a large percentage 
of the pods in contact with the ground became infected. 

Beet, Beta vulgaris 

Young seedlings of the garden beet, in flats, were found damping 
off in the vegetable-gardening greenhouses of the Station, July 10, 
1913. Cultures showed that B. Solani was the sole cause of the dis- 
ease. Characteristic lesions were found on the beets at the surface of 
the ground, and strands of myeolium could be plainly seen spreading 
out on the surface of the soil. 

As with root rot of other fleshy crops, the fungus gains its first 
held at the crown of the mature plant, which, as a rule, is just below 
the surface of the ground. The first evidence of the disease is a 
darkening of the leaf bases, followed by the rotting of the crown. 
The leaves retain their color for a long time, or until the leaf stalks 
rot off almost completely. With the rotting at the crown, the beets 
begin to crack from this point. While the tissues around the cracks 
remain firm, as a rule, for a long time, the crown is usually soft, a 
condition due to the entrance of other organisms. Lesions are some- 
times formed on the sides of the beets, often extending deep into the 
tissues. When weather conditions become unfavorable to the fungus, 
the rotting and cracking stops and the plant may recover from the 
attack. The disease is generally scattered thru the field, only a few 
plants in a given area being affected. 

Under the name RMzocfonia hetcp Kiihn, PammeF^ in 1891 de- 
scribed a root rot of sugar beets. He was the first investigator to re- 
port serious damage caused by Rhizoctonia in this country. Duggar^^ 
in 1899 regarded the root-rot disease of sugar beet due to Rhizoctonia 
as one of the important diseases of that plant. At the present time 
this disease is very widespread and is the cause of considerable loss, 
especially in irrigated regions. 



1916] 



Parasitic Ehizoctonias in America 



315 




Fig. 9. — Garden Beet Inoculated with Bhizoctonia Sulani from Carnation, 
Showing a Late Stage of Infection (Experiment 8) 

Damping-off of sugar-beet seedlings has been reported by Selby,^^^ 
from Ohio, and by Smith/^"^ from California. 



Begonia 

Mr. H. W. Anderson in 1911 found a number of begonia cuttings in 
the floricultural greenhouses that were dami)i)ig off badly because of 
Rhizoctonia infection. The symptoms were similar to those described 
for cuttings of alternanthera. 

Damping-off of begonia cuttings has also been observed in New 
York by Duggar and Stewart,^- and in North Carolina by Stevens and 
Wilson.122 

Blackberry, Buhus sp. 

Root disease of blackberry and raspberry caused by Rhizoctonia 
has been reported only once in this country. Paddock "'^^ of Colorado, 
who studied this disease, described it as follows : 

' ' The trouble was first noticed by the foliage becoming light green or yellow- 
ish. Later in the season leaves on occasional plants began to curl and shrivel as 
parts of the plant below ground were attacked, but the greatest injury occurred on 
the canes above the crown. Here the bark was discolored and shrunken from the 
crown to the surface of the soil, or a short distance above. The fungus grew out 
within the bark, destroying the tissues, and interfering with the movements of 
jilant food. The injury commonly extended around the cane, and when it became 
deep enough to cut off the supply of moisture and food, the i^lant died." 

Buckwheat, Fagopyrum esculentum 

In 1911 Stevens and Wilson^-'^^^i mentioned a serious outbreak of 
Rhizoctonia on buckwheat in the western part of North C'arolina. No 
description of the disease was given. 



316 



Bulletin No. 189 



[June, 



Cabbage, Brassica oleracea 

Atkinson,'* in 1895, in his article on damping-off diseases, men- 
tioned cabbage seedlings as being susceptible to damping-off by Rhi- 
zoctonia. 

Duggar and Stewart^ ^ jj^ 1898 received from Illinois specimens 
of cabbage seedlings which had been diseased by Rhizoctonia. They 
found that the disease sometimes affected very young seedlings, caus- 
ing damping-off, but that it was more common after the plants had 
developed one or two true leaves. In the latter instances, small lesions 
at or below the surface of the soil characterized the disease. Later, 
Duggar and Stewart found 
Rhizoctonia causing a sim- 
ilar disease of cauliflower 
seedlings in New York. 
The plants showed ulcera- 
tion at the bases of the 
stems, the entire cortex in 
some cases having disap- 
peared. 

Fawcett^" reported a 
stem rot of cabbage seed- 
lings due to Corticium va- 
gum B. & C, in Florida, in 
1909. According to his 
description, the disease 
was a typical stem rot, 
with a softening of the epi- 
dermis followed by a shriv- 







Fig. 10. — Stems of Young 
Cabbage Plants Inocu- 
lated WITH Bhizoctonia 
Solani from Carnation 



Fig. 11. — Stem of an Old Cabbage 
Plant Which had been Placed in 
A Bench Infected with Bhizoc- 
tonia Solani from Carnation (Ex- 
periment 9) 



1916] Pakasitic Rhizoctonias in America 317 

(.'liiip of the outside tissues and a browning of the leaves. However, 
the plants so affected did not wilt down entirely, and many of them 
recovered. 

Candytuft, Ibcris sp. 

During June, 1914, a few plants of candytuft that had been grow- 
ing in three-inch pots in the floricultural greenhouses, rotted off at the 
surface of the ground. The symptoms were similar to those described 
for sweet alyssum. Microscopic examination of diseased tissue re- 
vealed R. Solani in every case. Dense masses of hyphai covering the 
leaves and stems of these plants were plainly visible. 

Duggar and Stewart^- in 1901 reported damping-off by Rhizoctonia 
of cuttings of candytuft in New York. 

Carnation, Dianthus caryopJiyllus 

Rliizoctonia Solani attacks carnation plants of all ages, both in the 
field and in the greenhouse, causing not only stem rot, but damping- 
off of cuttings, of which it is one of the principal causes. 

The symptoms of stem rot of carnation are very characteristic of 
the effects of R. Solani (Fig. 1). The fungus usually attacks the 
stem of the plant at the surface of the ground or occasionally just 
above or below. As a rule, the first indication of the disease is a pale 
green color of an entire plant or of a single branch. This lighter color 
can be noticed in most cases for several days before the actual wilting 
takes place. During cloudy weather the plant does not wilt for two 
weeks and sometimes for even longer, altho the stem may be almost 
completely rotted ; in sunny weather wilting occurs much sooner. 

If the stem of a plant that shows the first sign of wilting is pressed 
just at the surface of the soil, a soft place is felt and a slight twist is 
sufficient to slough off the bark. Beneath this is a slimy, wet area, 
which gives this rot its characteristic name. Sometimes, however, the 
stem is dry at the point of attack, and upon being broken off, the fibers 
appear to be separated and stringy. 

The fungus enters the cracks in the corky layer of the bark and at- 
tacks the cambium layer, causing the sloughing off of the bark. It 
then penetrates the woody tissues, and can be found even in the pith. 
The plant may remain alive after the cambium layer is destroyed until 
the fungus plugs the vessels. If a diseased plant is left in the soil for 
some time, the mycelium overruns the stem, and dark, round sclerotia 
are formed either directly on the bark or in the crevices, or cracks. 

The Rhizoctonia disease of carnation has been known to florists 
ever since carnations have been grown as a commercial crop in the 
greenhouse. In Volume I of the American Florist, 1886, is found the 
following paragraph, which is proba])ly the first published statement 
concerning the stem rot of carnation in this country. 

" In a few days plants began to show signs of wilting, and upon examination 
I found them rotted off just at the top of the ground, tho half an inch under 
the ground the stems appeared perfectly healthy." 



318 



Bulletin No. 1S[) 



\ J line, 




1916] Parasitic Ehizoctonias in America 319 

While the cause of the disease was not known at that time, from 
the description of the symptoms it is not to be doubted that it was due 
to Rhizoctonia. 

A great loss of plants from stem rot occurred thruout the country 
about 1900. Below are given a few excerpts from notes on this dis- 
ease which have appeared during the last thirty years, some of which 
agree with our present-day ideas : 

1886. "Deep planting causes the disease in many houses." 

' ' In our opinion high temperature and deep planting have much to do with 
the disease. ' ' 

1898. ' ' The most dangerous disease that attacks the carnation. Some varie- 
ties appear more subject to this disease than others, and there is considerable 
complaint about Flora Hill and Silver Spray this seas^on. The most common 
error that very often leads to this disease is too deep planting. The plants shoidd 
never be planted deeper than they stood in the field, preferably not so deep. The 
stem of the plant !-hould be out of the ground sufficiently to hold the branches 
away from the soil. I believe this disease is not found on carnations alone, but 
on other plants too, and the spores of this fungus may have been embedded in the 
soil, carried over or imprisoned, dormant in the plant from the cutting bench. 

' ' To check and prevent the spreading of this disease, dust flour of sulfur 
over the plants, and shake them so it will lodge on the stem and branches and on 
the soil around the stem. ' ' 

1900. "Climatic conditions rather than anything else are the chief causes of 
the trouble. High ranges of temperature whether in the cutting bench, field, or 
house, the results are the same, the amount of rot varying with preceding condi- 
tions. Thus, after heavy rains inducing soft growth, a rise of temperature into 
the 90 's is a capital condition for the development of stem rot. Some varieties 
are also more susceptible to attacks than others, the woodier ones being able to 
withstand it more than those of soft growth. ' ' 

1904. ' ' Stem rot is due to allowing plants to become pot-bound. 

' ' Eich soil with too much manure causing a rapid growth causes stem rot. 
I believe this to be responsible for more stem rot than all other conditions com- 
bined. Too deep planting also favorable for stem rot. Water when absolutely 
necessary and then water thoroly. ' ' 

190(3. "Presence of wounds on the bark, or punctures made by insects; 
faulty planting; sour or too highly enriched soil; lack of drainage; careless cul- 
tivation; lack of fresh circulating air; the maintenance of too great heat com- 
bined with atmosphere heavily charged with stagnant moisture during the time 
when the outdoor stocks are housed, will cause stem rot to become severe in the 
benches. ' ' 

1907. "Stem rot is the most dreaded and only disease of carnations in Ihe 
South. ' ' 

1909. ' ' Stem rot more dreaded in South than in North. ' ' 

1911. "Fresh air, plenty of circulation, a sweet soil, and proper watering 
will avoid to a great extent the appearance of stem rot or stop its spread. Weather 
conditions seem to play an important part, and in most cases as soon as cold 
nights are the rule, our troubles grow less. The greatest benefit is derived thru 
a clear and rather dry atmosphere. Deep planting not so important. Too much 
manure not necessarily a cause of stem rot. 

' ' Stem rot is more prevalent in sour soils than others. The surface of the 
soil should be kept open by frequent scratching. A dry interior and a wet surface 
is very conducive to stem rot. ' ' 

1913. "Stem rot in the South is more serious than in the North." 

The following older carnation varieties have beeen reported as being 
especially susceptible to stem rot : La Purite, Crimson King, De Graws, 
Sewan, Flora Hill, Silver Spray, McGowan, Portias, Scott, Jubilee, 



320 Bulletin No. 189 [June, 

Craig, Boston Market, Crane, Lawson, Ladj' Bountiful, Winsor. Sev- 
eral of these varieties are still propagated by a few growers and with 
good success, but the majority of them have been discarded. Of the 
newer types no one seems to be more susceptible than the others. 

To Duggar and Stewart^*^ is owed the discovery that Rhizoctonia 
is the cause of stem rot of carnation. This they proved conclusively 
in 1899 by inoculation experiments with pure cultures, repeated many 
times. Duggar and Stewart state that this stem rot is one of the most 
troublesome of the carnation diseases and probably occurs thruout the 
United States wherever the carnation is grown. Stewart^23-i24 g^^ ^^q 
same time distinguished between two distinct diseases, both called 
' ' stem rot. ' ' One is caused by Rhizoctonia, and the other by Fusarium. 

Card and Adams^^ of Rhode Island studied methods of control of 
both Fusarium and Rhizoctonia rots. They came to the conclusion 
that the use of clean, fresh sand in the cutting bench helps to control 
the fungus. They also found that stable manure does not favor the 
spread of the disease. 

In 1902 Stone and Smith^^^ reported carnation stem rot in Massa- 
chusetts. Two years later Clinton^'* reported the presence of the 
disease in Connecticut. In 1906 Heald^'^ stated that it was found in 
the field and in the greenhouse near Lincoln, Nebraska. Blake and 
Farleyi^ in New Jersey conducted a number of soil experiments for 
the control of stem rot. 

Carrot, Daucus carota 

Occasionally R. Solani causes damping-off of carrot seedlings, 
but the plants seem to be more susceptible later, when the fleshy root 
is formed. Here the rot starts at the crown and works up into the leaf 
bases. It also progresses into the interior of the fleshy root, as a rule 
showing no signs on the exterior for some time. In some cases lesions 
are found on the exterior of the carrot and on the larger secondary 
roots where they branch from the fleshy part. 

Duggar and Stewart^ ^ were the first to find a disease of carrot due 
to Rhizoctonia. In 1911 Heald and Wolf^^ reported from Texas the 
Corticium stage of the fungus on carrot. They stated that the roots 
were covered by white, ropy strands of the fungus, but that no serious 
rotting was observed. 

Celery, Apium graveolens 

A damping-off of celery seedlings in flats by RJiizoctonia Solani has 
been observed in the Station vegetable-gardening greenhouses. The 
symptoms are similar to those described for beets. 

During a search in the market in the winter of 1914 for leaf spot 
and soft rot on celery, several bunches shipped from New York were 



1916] Parasitic Ehizoctonias in America 321 

found to have a brown mycelium, and many small sclerotia between the 
stalks near the base. The fungus was causing no injury to the celery. 
When examined in the laboratory, the mycelium and sclerotia proved 
to be those of Rhizoctonia. Pure cultures of the fungus were obtained 
readily from the sclerotia. Repeated examinations of new shipments 
of celery from New York showed that in the majority of cases Rhizoc- 
tonia was present between the stalks. 

Duggar and Stewart^- in 1901 were the first to report Rhizoctonia 
causing a destructive damping-off of celery seedlings. Rolfs^^ in 1905 
reported a damping-off of seedlings in Florida caused by Corticium 
vagum B. & C. Van Hook^-'*^ found a Rhizoctonia associated with a 
root rot of celery in the field. He did not believe, however, that this 
fungus was the cause of all the trouble. Affected plants never attained 
full size, and an examination of the roots showed considerable decay. 
The disease seemed to affect the main roots, which rotted off rapidly 
near the crown. The fact that seed beds in new soil did not entirely 
control the trouble showed that the fungus Rhizoctonia was present in 
the new soil, tho not in any great amounts. Halligan,^^ in Michigan, 
has also studied the damping-off of celery plants in the seed bed. 

Centaurea gymnocarpa 

In the spring of 1914 a large number of seedlings of Centaurea 
gymnocarpa, including some of those which were potted, damped off. 
By June many of the potted plants were dying with stem rot, the dis- 
ease having been carried over on affected seedlings and in a few cases, 
no doubt, on healthy ones. Microscopic examination and pure cultures 
showed that in each case R. Solani was present in the diseased tissues. 
The progress of the disease was rather typical. The first symptom 
was the wilting and drying up of the foliage. On pulling up the 
plant, a number of the leaves were seen to be rotted off at the crown, 
while the bark on the stem below the surface of the ground sloughed 
off and the tissues beneath were wet and stringy. 

Clover, Red, Trifolium pratense 

In the spring of 1914 damping-off of red and Japanese clover was 
observed in the agronomy greenhouses. A culture easily obtained 
from the fungus appeared to be the same in all respects as the one 
isolated from alfalfa seedlings which were growing under similar con- 
ditions in close proximity. 

Stevens and Wilson ^^^ in 1911 reported that in a field of clover in 
North Carolina the roots were being attacked by Rhizoctonia and were 
suffering some damage. This is the only instance in which Rhizoctonia 
has been reported as injuring clover in the field. 



322 Bulletin No. 18i} [June, 

CoLEUS, Coleus sp. 

In November, 1912, cuttings of coleus began to damp off in a bench 
in the floricultural greenhouses. The variegated green varieties seemed 
more susceptible to the fungus than the variegated red and yellow. The 
trouble was found to be due to R. Solani. The infected cuttings showed 
characteristic lesions on the stems at the surface of the sand. These 
lesions were quite large and distinct, brown in color, and depressed 
several millimeters at the center. They were generally found on one 
side, but in some cases the whole cutting was girdled. Practically all 
the coleus cuttings in the bench damped off in this manner. 

During October, 1913, Rhizoctonia was found causing a damping- 
off of coleus seedlings planted very close in flats. About half the plants 
damped off. I 

Duggar and Stewart''- reported a dami)ing-off of coleus cuttings 
in New York, caused l)y Rhizoctonia, similar to that observed at this 
Station. 

Coniferous Seedlings 

The first case reported of damping-off of white-pine seedlings due 
to Rhizoctonia was by Duggar and Stewart,^^ from New York. Ten 
years later Clinton^'^ mentioned the damping-off of a number of conif- 
erous seedlings. 

Hartley, ^^ who made a study of the damping-off of coniferous seed- 
lings in the West, found that Rhizoctonia is one of several organisms 
involved. He wrote as follows : 

"Ehizoctonia (probably Corticium vagum B. & C), which onuses damping-off 
of very young seedlings, sometimes continues to work in patches till the plants are 
two months old or even more. On sandy soil, when seedlings from five to nine 
weeks old are killed, the youngest and deepest parts of the roots are usually first 
attacked. At Halsey, roots of Rocky Mountain yellow-pine seedlings about seven 
weeks old have been attacked at points as much as eleven inches below the ground 
surface. In many plants as old as this the older parts of the roots resist the en- 
trance of the fungus which has rotted the younger parts and Ihrow out new root 
branches, so that recovery takes place without any evidence of the damage being 
shown by the plant above ground." 

Coreopsis lanccolata 

Duggar and Stewart"'- in 1901 mentioned the fact that next to a 
plot of sweet williams that were being killed by Rhizoctonia, were two 
rows of Coreopsis lanceolata which were also diseased. They stated 
that ' ' only a few plants were killed, but from many of them the lower 
leaves had rotted away. The rot seemed to start in the base of the 
petiole, where it came in contact with the soil. The decaying leaves 
were overrun with Rhizoctonia." 



JD16] 



Parasitic l^mzorroNiAs in America 



323 



Corn, Zea mays 

In 1914, during the progress of the soH survey foi- R. Solani, the 
fungus was found frequently on corn roots in the field. It could not 
be determined whether the fungus penetrated the roots or not, but 
there was no question as to the abundance of the mycelium on the 
roots. 

Rolfs^^ in 1905 reported Corticium vugum B. & C. on corn in 
Florida. 

Cotton, Gossypium. Jierhacsum 



Glove]'^" in 1855 described a 
respects is the same as the disease 




Fig. 13. — Stems of Young Carna- 
tion Plants Inoculated with 
Ehizoctonia from Cotton, 
Showing Lesions Characteris- 
tic OF Sore Shin of Cotton 
Caused by the Same Fungus 



sore shin of cotton, which in some 
of seedling cotton caused by Rhizoc- 
tonia. He stated that ' ' the cause is 
attributed by many to cold, cutting 
winds, when the plant is very 
young. Others, however, assert that 
when a high wind shakes a tender 
plant, the main stem is so much 
bent and twisted that the sap ves- 
sels are upturned and a serious in- 
jury occurs." 

One of the causes of sore-shin 
disease of cotton remained undis- 
covered until Atkinson,^' in 1896, 
found in the diseased tissues a ster- 
ile mj^celium, which he later identi- 
fied as Rhizoctonia. By means of 
pure-culture methods and inocula- 
tion experiments he further proved 
that this sterile fungus was the 
cause of sore shin and also of seed- 
ling rot and damping-off of cotton. 
He describes the Rhizoctonia dis- 
ease of cotton as follows : 



"There are several phages of the disease. Sometimes the tissues undergo a 
soft rot which progresses very rapidly, and the early stages are not marked hj any 
striking color characteristics. Another phase may j^rogress rapidly or slowly and 
is usually quite well characterized hj a reddish brown color which accompanies it. 
This phase is also characteristic in that it is usually manifested on one side of 
the stem in the form of an ulcer which gradually deepens until the vascular sys- 
tem is reached, when the life of the plant becomes really endangered. Even when 
this stage is reached, however, the plant may, and does frequently, recover. 

"This latter phase is chnracteristic of a very common disease of seedling 
cotton. It is called by the planters in mony places 'sore shin.' 

"The diseased portion of the plant is just beneath the surface of the ground 
and presents an area of shrunken tissue of a dull brown or reddish color. The 



324 Bulletin No. 189 [June, 

size of the shrunken area and the depth of the injury are proportionate to the 
serious condition of the ulcer, as it may be termed. If the injury remains con- 
fined to the superficial tissues, the plant will usually recover. It does sometimes 
recover when the injury reaches the vascular tissue, but more frequently death 
results when the trouble has progressed thus far. ' ' 

No further original work has been done on this disease since the 
time of Atkinson, altho several of the southern experiment stations 
have published bulletins on cotton diseases, including the sore shin 
and seedling rot due to Rhizoctonia. 

DiantJiiis 

R. Solani was isolated from diseased plants of Diantlius harhatus 
(Newport Pink), during July, 1913, in the perennial garden of the 
Station. This variety and DiawtJius harhatus (single mixed) were 
much more susceptible to stem rot than were any of the other varieties 
grown. In fact, practically every plant of these two varieties died 
from stem rot during the summer. These varieties are more like the 
carnation than any of the others, and when affected, the symptoms of 
the disease were very similar to those of stem rot of carnation. The 
first evidence of the disease was the pale green color of the leaves, 
followed in many cases by a sudden wilting of the foliage. When 
plants in this stage were pulled up, the bark readily sloughed off, 
leaving the wood exposed. When plants in the later stages of the 
disease were pulled up, the stem usually broke off at the surface of the 
ground, exposing stringy tissue. 

During the same month, a disease of Biantlius sequeri and D. 
plumarius was under observation. Diseased parts of these plants 
yielded Rhizoctonia in every instance. In the case of D. sequeri the 
fungus seemed to be living saprophytically among the numerous pros- 
trate, bushy branches. The brown strands of the mycelium could be 
plainly seen running thru the bushy mass of the plant. Only a few 
plants died. Unlike the case of D. harhatus, there was no characteris- 
tic sloughing off of the bark, but a more or less general rotting of the 
whole stem, which left the tissues very dry and stringy. The attack 
was not confined to the main stem, but affected any of the branches 
which touched the ground. 

Most of the plants of D. plmnarius, occupying a space about three 
feet long, died from attacks of the fungus. The symptoms of the dis- 
ease were very similar to those of D. sequeri, the rotting appearing 
to extend gradually from one point thru the whole stem. As with D. 
sequeri also, the bushy habit of the plant gave ample protection to the 
fungus, and the radiating strands of the brown mycelium of Rhizoc- 
tonia were visible to the naked eye. 

_ Duggar and Stewart^s in 1900 found a badly diseased plot of 
Diantlius harhatus in which 90 percent of the plants, in the course 
of the season, died from stem rot due to Rhizoctonia. 



1916] Parasitic Ehizoctonias in America 325 

Eggplant, Solarium melongena 

During August, 1912, while some field observations were being 
made on carnation stem rot, the fruits of a number of eggplants in 
an adjoining field were found to be rotting at the point where they 
touched the ground. The decay spread in all directions from this 
point, making a sunken, brown area; this was followed by the soften- 
ing and subsequent collapse of the surrounding tissues. Fruits showing 
this decay were brought into the laboratory and placed under a bell 
jar. Around the diseased spot there soon developed a thick mass of 
mycelium, which on microscopic observation was found to consist of 
hyphae of Fusarium and Rhizoctonia. The decaying spots contained 
no fungous threads, but were completely filled with bacteria. On plat- 
ing, pure cultures of R. Solaiii were obtained. The cause of the pri- 
mary infection is not known. It is very probable that both the Fusar- 
ium and Rhizoctonia entered the tissues where the epidermis had been 
destroyed. 

In July, 1913, the damping-off of a number of eggplant seedlings 
in the vegetable greenhouses was noticed. This was shown, by pure 
cultures of the diseased material, to be due entirely to Rhizoctonia. 
The fungus produced the characteristic lesions on one side of the seed- 
lings at the surface of the soil, causing the stem to break. 

Atkinson,"* in his account of damping-off diseases, mentioned 
eggplant seedlings among those susceptible to attacks of the sterile 
fungus (Rhizoctonia), Rolfs^^ reported the presence of the Corticium 
stage of Rhizoctonia on mature plants in an irrigated garden. Here 
the plants affected drooped for a time and then wilted and died. Le- 
sions were formed on the stems at the surface of the ground. 
^Qlfi4o-i4i jj;^ 2914 reported damping-off and a fruit rot of eggplants 
due to Rhizoctonia {Corticium. vagum B. & C), but he does not re- 
gard the fungus as the cause of serious injury to eggplants. 

FivE-FiNGER, Potentilla sp. 

A number of five-finger plants were found to be infected with 
7?. Solani during June, 1914, in inoculated sections in the fioricul- 
tural greenhouses. The mycelium of the fungus was present at the 
nodes which touched the soil and also at the bases of the plants, where 
crown rot was developing. 

Foxtail Grass, Setaria glauca 

Several plants of foxtail grass growing under the same conditions 
as the prjBceding host, five-finger, showed a root infection. 

GypsopJiila repens 

A number of GypsopMla repens plants were found diseased in the 
herbaceous grounds during July, 1913. Pure cultures of the diseased 



326 Bulletin No. 189 [June, 

material showed the causal organism to be Ii. Solani. The plants were 
bnshy, so that some of the branches and leaves were in contact with 
the soil. The symptoms and appearance of the disease were similar 
to those described for Dianthus. 

Lamb's Quarters, Clienopodium album 

During the summer of 1913 several wilted Clienopodium plants 
were observed along the border of the old herbaceous grounds of the 
Station. On pulling up the wilted plants, it was found that R. Solani 
was the cause of the wilting. The fungus did not enter very deep 
into the tissues, but rather girdled the stem and formed a scurfy layer. 

Duggar and Stewart'*- in 1901 reported the occurrence of Rhizoc- 
tonia on Clienopodium album. 

Lavatera arborea variegata 

During March, 1913, in the floricultural greenhouses, a number of 
seedlings in small seed pans, among which were several pans of Lava- 
tera, began to damp off in a manner characteristic of R. Solani. 
Pure cultures of diseased seedlings yielded this fungus. Strands of 
the brown mycelium could be seen on the surface of the soil and 
extending up on the stems and leaves. This was noticed again in the 
spring of 1914. 

Lettuce, Lactuca sativa 

Atkinson^ in 1895 mentioned the damping-off of seedling lettuce, 
among a number of other plants, by a sterile mycelium which later 
proved to be Rhizoctonia. 

Stone and Smiths -^ found that R. Solani caused a rot of green- 
house lettuce, altho the disease was not common. The first appearance 
was on the lower leaves where they lay on the ground; a brown rot 
set in, which spread thru the leaf in a very characteristic manner. 
The green blade rapidly rotted away, leaving the midrib and stalk as 
sound as tho the blade had been carefully cut away or had been eaten 
by insects. 

Duggar and Stewart^- observed the damping-off of lettuce seed- 
lings by Rhizoctonia for a number of yeare. They found that at or 
near the surface of the ground the tissues become water-soaked in 
appearance and unable longer to support the seedling, so that it falls 
to the ground, the fungus invading all j^arts. Within a day or two 
this fungus, under favorable conditions, wilted down and destroyed 
whole boxes of lettuce seedlings. Duggar and Stewart also observed 
several times what was apparently the same fungus causing a disease 
of mature lettuce plants. On the older leaves the leaf blades alone 
were affected, but the more delicate inner leaves succumbed entirely, 
blackening and decaying with the progress of the disease. 



1916] 



Parasitic Ehizoctonias in America 



327 



In 1903 Selby^*^^ reported the })i'csenee of a rosette disease of let- 
tuce, which he described as follows: "The plants affected showed, 
usually not long after transj)lanting, but occasionally at other stages, 
a failure to send out central leaves freely. The leaf -bearing axis re- 
mained shortened, and the last leaves formed remained short, making 
a very striking contrast to the remainder of the plants in the bed 
and to the lower leaves of the same plant. (Frequently the plants 
overcome this tendency and make a fair amount of product with 
longer time.) Examination of the roots showed areas occupied by 
the hyphae of Rhizoctonia. " In 1906 Selbyi^*^ treated at length the 
control of rosette in lettuce due to Rhizoctonia. 




Fig. 14. 



-Dampixg-off of Lavatera Seedlings by Bhkocionia Solanl 
(Experiment 9) 



328 Bulletin No. 189 [June, 

In 1905 Rolfs^^ reported the presence of the perfect stage, Cor- 
ticium vagum B. & C, on lettuce from Florida. 

Lobelia erinus (Single Blue) 

The lobelia plants in the floricultural greenhouses in 1914 were 
small and sessile, and covered the tops of the pots in which they were 
growing. In June a number of them began to die. On close exami- 
nation, strands of B. Solani could be seen spreading thru the mass of 
plant material. The low-lying leaves afforded a good hiding place 
for sow bugs, and no doubt they helped in carrying the fungus from 
one pot to another. Attacks of Rhizoctonia on other varieties of lobelia 
liave been observed in the greenhouses a number of times. 

Onion, Allium sp. 

A culture of Rhizoctonia isolated from onion seedlings was ob- 
tained from Cornell University by Mr. H. W. Anderson in 1911. Since 
that time the author has worked with this strain both in the laboratory 
and in the greenhouse. From its morphological and physiological 
behavior, it must be classed as distinct from the other strains. 

Dr. I. G. Jagger states in a letter that he first isolated this form 
from onion on May 29, 1911, from seedlings growing on muck soil in 
New York. He found that the Rhizoctonia mycelium was always con- 
fined to the first, or seed, leaf and that damping-off ceased as soon as 
the second leaves had developed. 

Pansy, Viola tricolor 

During the fall of 1913 pansy plants were placed in a solid bed, 
in the floricultural greenhouse, as a border for sweet peas. At that 
time some of the sweet-pea plants died, and eventually a culture of R. 
Solani was obtained from them. The following April several pansy 
plants in the vicinity of the spot where the sweet peas had died became 
diseased and later died. A culture shoAved the trouble to be due to 
Rhizoctonia. Later a large number of the plants in the row died. The 
fungus attacked the plant at the crown and caused a rapid rot. The 
prostrate branches, the petioles of the leaves, and even the leaves them- 
selves were also rotted in a characteristic fashion. The strands of the 
mycelium could easily be seen ramifying between the rotting mass 
and the soil. 

Plantain, Plantago aristata 

Diseased plants of plantain were found during June, 1914, in 
inoculated sections in one of the floricultural greenhouses. The 
mycelium of R. Solani was present around the bulbous base of the 



1D16] Tarasttic RHizorTONiAS IN America 329 

plants, causing a crown rot. In one or two cases several leaves were 
completely rotted at the crown. 

PoiNSETTiA, Euphorbia pulcJierrima 

About October 7, 1912, young poinsettia plants were taken from 
the cold house (50° to 60°C.) of the floricultural greenhouses and put 
in a box with a glass top. They were then placed near the cutting 
bench, in which a number of plants of various kinds were damping off. 
The poinsettia cuttings shortly afterwards began to die off rapidly. 
The characteristic lesions on the stems of the young plants and pure 
cultures of the diseased material indicated that this condition was due 
to 7?. Solani. The lesions, instead of being on one side and more 
or less localized, in almost every case formed a collar around the stem 
at the surface of the soil. The collar was about 2 to 3 millimeters 
wide, somewhat depressed, and of a dark color. Strands of the brown 
mycelium were visible spreading over the soil in the pots. This infec- 
tion probably had its origin in the cutting bench. 

Potato, Solanum tuberosum 

On the potato R. Solani exhibits a number of interesting charac- 
teristics, which vary with climatic conditions, age of the host, and part 
of the plant attacked. 

The sclerotial stage of this fungus has been observed on practically 
every Illinois potato tuber examined by the writer. Moreover, in 
every shipment from other states which has been examined, the fun- 
gus has been found present. The tubers affected were dotted with 
brownish black sclerotia of various shapes and sizes (Fig. 15), but so 
far as could be determined, they were causing no direct injury. This 
type of Rhizoctonia disease of potato is the one most commonly found 
in the United States. 

R. Solani also causes, under certain conditions, a russeting, or 
scab, a cracking of the tuber, the formation of pits at or near the len- 
ticels, and a wet rot of the tuber. These types of injury have been ob- 
served by Eolfs^^'^^ in Colorado, by Orton'^ in various states, and 
by Morse and Shapovalov^^ in Maine. 

On the plant itself this fungus produces various types of diseases. 
In many cases young plants are completely cut off before they reach 
the surface of the ground. Older plants that are severely attacked 
just below the surface of the ground usually die off quickly. If they 
are only slightly attacked, the fungus produces small lesions on the 
stems, the plants take on a dwarfed and unhealthy appearance, and 
the tubers remain small, altho the plants usually live thru the sum- 
mer. When the stem is girdled by the fungus so as to prevent trans- 
location entirely, large tops are produced, aerial tubers are formed, 



330 



Bulletin No. ISi) 



[June, 




Fig. 15.— Potato Tuber Showing the Sclerotia of Bhizoctonia Soluni 



1D16] I'AKASITU' IvHlZOI TONIAS IN AmEIUCA 331 

and in some eases a eurlino^ of the leaves or rosettinfi: results. When 
the main stem is attacked below the surface of the soil and the stolons 
are cut off, the conditiop known as "little potatoes" is produced; in 
such cases a cluster of small, short-stemmed tubers is formed above 
the wound. The production of aerial potatoes, rosette, and leaf curl- 
ing also occurs when the stolons are attacked and the young tubers are 
cut off. 

These abnormal developments of the potato are usually associated, 
and are secondary physiological effects due to disturbances of the 
nutrition of the plant. They occur most frequentl.y on poorly drained 
land and especially on heavy soils. 

Rolfs''- attributed the potato failure of 1902-03 in Colorado to 
little potato. Selby^*^" in Ohio, in his studies of the Rhizoctonia dis- 
ease oil potato, gave particular attention to rosette. In 1914 Morse 
and Shapovalov'''^ concluded that the Rhizoctonia disease of potato is 
of a more serious nature than is generally considered. In one field 
which they had under observation for several seasons, they attributed 
the poor and uneven stands, unexpected low yields, early ripening, 
and death of the tops to Rhizoctonia. In most cases they confirmed 
the observations made by Rolfs. Recently investigators all over the 
country have been emphasizing the serious nature of the disease. 

In January, 1915, material of BMzocioyiia Crocorum on potato 
tubers was received from Mr. F. D. Bailey of the Oregon Agricultural 
Experiment Station. On comparing it with Rliizoctonia Solani, it was 
found to be entirely different in all respects. However, this fungus is 
identical with the fungus on alfalfa reported by a number of observers 
(Webber, Heald, and Freeman) as R. Crocorum. Thus it appears 
that B. Crocorum is present in this country on alfalfa and on potato 
tubers. 

Bailey^ describes the Rhizoctonia disease of potato as follows : 

' ' The surface was almost entirely covered with a dense, felt-like mat of a 
chocolate color when dry, violet -brown when moist. This mat was found to be 
composed of mycelium which had long narrow cells and a branching habit char- 
acteristic of Ehizoctonia. The greater part of this mycelial mat could be easily 
removed, and beneath this the surface of the tuber was covered with very small 
dark spots. These spots appeared to the unaided eye as minute eruptions of the 
skin. Under the microscope one can se€ the mycelial threads attached at these 
points, and a freehand section thru such a spot shows it to be a structure com- 
posed entirely of interwoven fungus threads forming a sclerotium. No evidence of 
differentiation or any type of spore formation within this body could be found 
on examination of many sections. The portion of the sclerotium near the sur- 
face is composed of cells that are very deeply colored, giving the black appear- 
ance. The outer surface of the sclerotium is seen to project above the surface, 
while the lower or underlying jjortion is embedded in the outer cortical layers 
of cells of the tulier. Furthermore, there is a strand of fungus tissue extending 
deeper than the sclerotium, which connects it with a layer of the same type of 
fungus tissue spreading between the cortex and parenchyma from the point where 
this strand reaches the parenchyma. 

"Attempts to grow this fungus in culture failed. This has been the experience 
reported in attempts to grow Ehizoctonia violacea Tul. " 



332 



Bulletin No. 189 



[June, 



Radish, RapJianus sativus 

Damping-off of radish seedlings by R. Solani has appeared sev- 
eral times in the floricultural greenhouses. Diiring May, 1914, an at- 
tack of Rhizoctonia on mature radishes was observed in the writer's 
home garden. The first sign of the disease was the yellowing of the 
foliage, followed by the wilting of the leaves. On pulling up a 
plant, the crown was found to be rotted at the base of the leaves. The 
rot progressed slowly and killed only a few of the plants. After it 
had proceeded for some length, the radishes cracked farther down. 
This is very characteristic of the disease at this stage (Fig. 16). 

In 1895 the damping-off of radish seedlings by a sterile fungus, 
which was later identified as Rhizoctonia, was first reported by Atkin- 
son.'* Duggar and Stewart^- in 1901 noted a disease caused by Rhi- 
zoctonia of mature radishes forced in a greenhouse. The disease 
caused a soft rot of the crown or lesions in this region. The leaves 
were generally unaffected until a large part of the root had decayed. 
Plants in all stages of growth were affected and killed. Duggar and 
Stewart also found a Rhizoctonia in connection with the damping-off 
of radish seedlings in the greenhouse. 




Fiij,. IG. — Late Stage of Koot iiOT of Kadishes Caused by Bhisoctonia Solani 



1916] Parasitic Ehizoctonias in America 333 

In 1904 Clinton^ ^ observed a damping-off and root rot of radisli 
due to Rhizoctonia. Apparently the disease was not very serious. 
Stewart^ 2^ in 1910 also reported a damping-off and root rot of radish 
due to Rhizoctonia. Infection took place first at the level of the soil, 
causing the leaves to have a wilted, drooping appearance. From this 
point the disease spread into the leaves and roots of the plant, soon 
causing death. On mature radishes, decayed spots of irregular shape 
were produced, and at an advanced stage the diseased portions of the 
plant were covered with a white, felted mycelium. 

Rhubarb, RJieum rliaponticum 

In 1901 Duggar and Stewart^- reported a disease of rhubarb, on 
Long Island, which they had had under observation for several years. 
They described the disease as follows : 

"An unthrifty condition of the plants was noticed, followed by the rapid 
dying off of many of the leaves. The affected leaves became dry and shrunken 
in appearance and soon fell to the ground. Where a field was badly affected, 
the majority of hills showed the trouble to the extent of at least a leaf or two. 
In several instances from one-fourth to three-fourths of the leaves were already 
dead. An affected leaf breaks off readily just beneath the surface of the ground, 
and old dead leaves rotted off in this region. The general appearance reminded 
one strongly of the effect of Rhizoctonia upon beets. There was very little super- 
ficial mycelium visible to the unaided eye. Microscopic examination showed 
hyphse of a Rhizoctonia both superficially and immediately under the surface where 
the leaves were rotting." 

Clinton^^ has also reported a stem rot of rhubarb due to Rhizoc- 
tonia. He found the fungus at the base of leaf petioles, causing dark, 
sunken cankers. 

Salvia, Salvia splendens 

The symptoms of the Rhizoctonia disease of salvia observed in the 
floricultural greenhouses were similar to those described for coleus. 
All varieties of the cuttings in the bench seemed to be equally suscep- 
tible. It has been shown that the serious damping-off of the salvia, al- 
ternanthera, and coleus was due to the fungus which was first brought 
in on the mature alternanthera plants from which cuttings were made. 
(See Alternanthera, page 310.) 

Santolina cJiama'cyparissus 

In 1914 a number of plants of Santolina cJiama'cyparissus growing 
in pots next to the Gentaurea gyninocarpa in the floricultural green- 
houses, were found to have a typical stem rot, due to R. Solani, very 
similar to the disease as described for that plant (see page 321). The 
fungus could be distinctly seen running thru the bushy branches. 



334 Bulletin No. 189 [June, 

Sedum sp. 

A few plants of Sedum. anglicum, together with several other spe- 
cies of Sedum, were found diseased, in July, 1913, in the herbaceous 
grounds. The progress of the disease was very slow ; few plants were 
killed during the entire summer. For the most part, the fungus 
seemed to live saprophytically at the base of the plant. It was also 
found on healthy plants of this genus. About six species were planted 
in a row in the garden, and all Averc affected in much tlie same way. 

Sorrel, Rumex acetosella 

In June, 1914, a number of sorrel plants were found diseased in 
an inoculated section in the grcenliouse. The stems of the plants were 
covered with the ])rown strands of mycelium, and a few of the leaves 
were rotted oft' at the crown. Pure cultures of the diseased parts 
yielded R. Solani in every case. 

Sweet Pea, Latliyrus odoratus 

During July, 1912, when the young sweet peas in the field were 
about one-third to one-half grown, occasional vines showed evidence 
of disease by turning yellowish, wilting, and finally drjdng up en- 
tirely. An examination of the affected plants showed that they were 
more or less separated from their roots near the surface of the ground. 
Pure cultures of the diseased material yielded R. Solani in all cases. 

In November, 1913, several diseased seedlings were brought in from 
the plant-breeding greenhouses. On close examination the stems 
showed the characteristic lesions caused by Rhizoctonia. The same 
trouble occurred in the floricultural greenhouses the past two seasons, 
but in no case was it severe. 

During the winter of 1913, the writer was called to Chicago to look 
over a range of greenhouses devoted to the growing of sweet peas. 
Sweet-pea plants of all ages were seriously affected. Dead plants were 
scattered thru the whole house. Close examination of the diseased 
plants revealed the fact that Rhizoctonia was causing the trouble. 
Apparently it started in the seed pans and continued to work until the 
plants were ready to be discarded. The symptoms in each case were 
the same— yellowing of the foliage, followed by the wilting and dry- 
ing up of the plants. Characteristic lesions, which finally cut the 
stems off at the surface of the soil, could always be found on the dis- 
eased plants. The root systems were much dwarfed. 

In 1908 Clinton'*^ observed in Connecticut a damping-off of sweet 
peas due to Rhizoctonia. Taubenhaus^^'^-^^i in describing a Rhizoc- 
tonia rot of sweet pea at different stages, states that he found it quite 
destructive to the plants when they are in the seedling stage. 



HJIAJ] Parasitic Ehizoctomas in America 335 

Tobacco, Nicotiana sp. 

In 190-i Clinton^ ^ noticed a seed-bed rot of tobacco, which he 
thought was due to Rhizoctonia. The same year Selby^*^^ observed a 
similar bed rot of tobacco in Ohio caused by Rhizoctonia. He stated 
that the specific characteristics of the fungus do not differ essentially 
from those of its forms on other plants, including potato. 

Clinton,^ ^ in making another report on this disease, in 1906, stated 
that the injury to the plants was slight and was confined, as with the 
potato, to the underground parts. 

Johnson'^^ has carried on some extensive work on Rhizoctonia, with 
a ^'iew to controlling the damping-off of tobacco seedlings. 

Tomato, Lycopcrsicum escvlentum 

A damping-off disease of tomatoes caused by Rhizoctonia has been 
noted from a number of states ; the symptoms of the disease are the 
same as have been described for a number of other plants, such as 
eggplant. 

In connection with his work on the potato rosette resulting from 
Rhizoctonia, Selby^'^^ also mentioned a tomato rosette caused by the 
same fungus. He stated that the tips of diseased plants showed 
rather long internodes and dwarfed leaves, with somewhat curled-leaf 
aspects, while the roots had lesions and other similar features found 
in potato rosette. 

Rolfs''^ in 1905 stated that he frequently found the Corticium stage 
on the tomato plant, but that apparently the plants do not suffer ma- 
terially from its i)resence when planted on well-aerated land. He 
described it as follows : 

"The fruiting stage of the fungus develops freely on the stem just above the 
surface of the ground, often extending u|) the stem for a distance of six inches. 
As a rule the fungus docs not peiu^tratc the tissue here, but simply covers the stem 
of the plant. The tomatoes which touch the ground arc frequently more or less 
covered by a fruiting mendnane of the fungus, which mars the appearance of the 
ripe fruit. So long as the tomatoes are green and the skin uninjured, the fruit 
remains sound ; however, if the skin is ruptured, the fungus soon destroys it, pro- 
ducing a brown rot. This organism also frequently gains entrance to the fruit at 
the stem end. ' ' 

Orton"- described the rosette of tomato caused by Corticium vagmn 
B. & C. as a disease of minor importance in tomato culture. He stated 
that ' ' the fungus attacks the roots and base of the stem, forming dark 
cankers. The effect on the plant is to dwarf and curl the leaves and 
to restrict productiveness." 

A fruit rot of the tomato has also been observed by PooP*^ and 
again by Wolf.^^^ Pool described the symptoms of the fruit rot as 
follows : 

" Tlie specimen examined showed no rupture in the external skin visible to 
the naked eye. The diseased area was plainly distinguishable by the chocolate- 



336 Bulletin No. 189 [June, 

colored, slightly ■wrinkled epidermis. An examination of the underlying tissues 
revealed the same general color and numerous, somewhat darkened filaments pene- 
trating the cells in all directions." 

WoUenweber^^^ in 1913 described a species, RJiizoctonia poto- 
macen^is "Wr., which causes a fruit rot of green tomatoes. He stated 
that this species differs from RJiizoctonia Solani in the character of 
its attacks, in that concentric, subepidermal mycelial zones are formed 
within the tomatoes. 

Violet, Viola odorata 

During the fall of 1913 a number of violet plants in the floricul- 
tural greenhouses were found to be diseased. A few had stem rot, 
while on others only the bases of the petioles were somewhat rotted. 
Where the pots were set close together and the plants overlapped, the 
brown strands of R. Solani could be plainly seen spreading out from 
one plant to another. However, in no ease was the disease severe ; it 
is probable that the fungus was living saprophytically on the lower 
leaves. 

Duggar and Stewart" ^ observed, in a greenhouse in New York, one 
case of destructive violet stem rot due to Ehizoctonia and a second 
case similar to the attack described above. 

Additional Observations 

Beside the hosts that have been mentioned, observations have been 
made in the floricultural greenhouses of diseased seedlings and cut- 
tings of a number of other plants, tho no work has been done further 
than to make a microscopic examination of the diseased material. 

Below is a list of seedlings and cuttings found damping off in the 
spring and fall of 1914, with the percentage of loss resulting. In all 
cases Rhizoctonia proved to be the cause of the trouble. 

Percentage 
Seedlings Damping off, April 6, 1914 of loss 

Amaranthus caudatus 75 

' ' salicifolius .^ 90 

Bartonia aurea 90 

Calendula Pongei 1-2 

Celosia Huttoni, var. Thompsonii magnified 75 

Chrysanthemum hortorum 30-40 

Bianthus chinensis 80 

' ' Heddewigii 30 

' ' latifolius 80 

Godetia sp 80 

Gypsophila muralis 30 

Kochia trichophylla 99 

Lavatera arhorea variegata 5 

Linaria Maroccana 5 

JAnum grandiflorum rubrum. 30 

Lychnis coeli rosa 90 

Portulaca oleracea 80 

Schizanthus sp 2-4 



1916] Parasitic Ehizoctonias in America 337 

Percentage 

Seedlings Damping off, September 2, 1914 of loss 

Aquilegia (6 species) 85 

Campanula (8 species) 80 

Cineraria (several species) 20 

Dianthus plumarius 85 

Erysimum pulchellum 2 

Linaria Cymhalaria 2 

Lythriim sp 2 

Matthiola incana (stocks) 2 

Primula malacoides 2 

' ' obconica grandifiova 2 

Schizanthus (mixed) 2 

Silene Schafta 100 

Stachys lanata 2 

Viola tricolor (3 varieties) 20 

Cuttings Damping off, September 25, 1914 

Abutilon hybridum, var. Savitsii 100 

Acalypha Wilkesiana, var. bicolor 100 

" " " tricolor 100 

" " " marginata 90 

Ageratum mexicanum vars 2 

Alyssum odoratum (3 varieties) 100 

Coleus ( 10 varieties) 2 

Cuphea platycentra 2 

Iresine (Achyranthes) (5 varieties) 95 

Petunia (several varieties) 100 

Piqueria trinervia {Stevia) 100 

Santolina cTiamcecyparissus 2 

Sedum spectabile 2 

Telanthera (Alternanthera) (9 varieties) 2 

Vinca major (several varieties) 2 

Types of Symptoms 

From a study of the symptoms caused by RJiizoctonia Solani on 
the various hosts, it is seen that, except for a few minor points, they 
are the same when appearing on the same type of host. The damping- 
off of seedlings and cuttings of various plants is identical, as is the 
rotting of a number of root crops. In most herbaceous plants a stem 
rot is produced, the symptoms of which arc also identical on the vari- 
ous hosts. On very resistant plants lesions only are formed ; these are 
apparently identical on the different hosts. 

INOCULATION EXPERIMENTS 

The main purpose of these inoculation experiments was to ascer- 
tain the degree of biologic specialization which may exist between the 
various cultural strains of Rhizoctonia, or between strains isolated 
from different hosts or of different geographical origin. With three 
thousand square feet of glass available in the floricultural greenhouses 
and with the assistance of the members of the floricultural division, it 
was possible to carry on cross-inoculation experiments involving about 



338 Bulletin No. 189 [June, 

3,000 cuttings, 2,000 plants, and 7,000 sefJlings of various kinds. With 
these, comparisons Avere made of about forty-five strains of Rhizoctonia. 
A large number of the strains used in these experiments were iso- 
lated by the writer from the various hosts found infected with Rhizoc- 
tonia in this vicinity. Other strains were obtained from various in- 
vestigators thruout the country. Below is presented a list of the strains 
used and the source of each. 

Alfalfa. — A Ehizoctonia culture from alfalfa was received from Dr. C. VV. 
Edgerton, Baton Eouge, Louisiana, November 12, 1912. It was originally ob- 
tained by Dr. Edgerton in May, 1910, from alfalfa seedlings. 

Alternanthera B.A.C. — A culture of Ehizoctonia was isolated from infected 
alternanthera cuttings found in the floricultural greenhouses in the fall of 1912. 

Alternanthera B.A.F. — This strain was obtained at the same time as the 
preceding, from mature alternanthera plants in the field. 

Amaranthus. — In August, 191.3, Mr. W. H. Burkholder, of Cornell University, 
contrilmted several specimens of Amarantlms retro flexus infected with Ehizoc- 
tonia, from Irving, New York. The stems were covered with the immature, gray, 
felt-like mycelium of the Corticium stage. Scrapings of the hymenial layer of 
this stage yielded pure cultures of Ehizoctonia in every case. 

Aster. — Early in 1913, Dr. F. A. Wolf sent to the writer a culture of Ehizoc- 
tonia which was the cause of the damping-off of China aster seedlings in flats 
in the greenhouse at Auburn, Alabama. 

Bean. — A transfer of a culture of Ehizoctonia from bean was obtained in 
December, 1912, from Dr. J. T. Barrett, of this university. He in turn had re- 
ceived it from Dr. M. F. Barrus, of Cornell University, about 1910. 

Beet. — A culture of Ehizoctonia was obtained from young seedlings of the 
garden beet found damping off in the vegetable-gardening gieenhouses, July 10. 
1913. 

Begonia. — The strain from l>egonia was isolated by Mr. Anderson from cut- 
tings found damping off in the floricultural greenhouses in the fall of 1911. 

Carnation. — During the season of 1911-12, Mr. Anderson isolateil Ehizoctonia 
from a number of carnation plants received from different sources, and during 
1912-13 and 1913-14 the work was continued by the author, so that a comparison 
of a large number of cultures from diseased plants obtained from various localities 
was possible. The strains used are given below. 

"Carnation E.K. ": Isolated by Mr. Anderson from diseased carnation 
plants obtained at Urbana, Illinois, in October, 1911. 

"Carnation E.O. ": Culture isolated by Mr. Anderson in the fall of 1911, 
at Urbana. 

"Carnation E.H.'": Culture isolated from a diseased plant in the floricul- 
tural greenhouses in the fall of 1911 by Mr. Anderson. 

' * Carnation E.S. ' ' : Isolated from diseased plants received from Kankakee, 
Illinois, by Mr. Anderson, October 25, 1911. 

' ' Carnation E. 2 " : Culture reisolated by Mr. An<lerson from infected cut- 
tings in sterilized soil in the spring of 1912. 

"Carnation E.F. ": Isolated from diseased carnation plants gathered in the 
field in the horticultural grounds, July 24, 1912. 

"Carnation E.M.2": Isolated from a White Enchantress plant in one of 
the floricultural greenhouses during September, 1912. 

"Carnation E. 107": Obtained from a j^lant in the floricultural greenhouses, 
September 7, 1912. 

"Carnation E.F.2": Culture obtained from a diseased plant in the field 
during the summer of 1913. 

"Carnation E. 121-5": A reisolation of Ehizoctonia was obtained on De- 
cember 3, 1912, from a diseased plant in one of the inoculated sections of the 
greenhouse. 

Carrot. — Tlie strain of Ehizoctonia from carrot used in this work was ob- 
tained by Mr. Anderson from Cornell University in 1911. Nothing is known of 
the origin of the culture. 



1916] Pauasitic Khizoctonias in America 339 

Caiilifloircr. — A eiiltuie of Rhizoctonia from oanliflower was ol)taiiiO(l in 1912, 
from Dr. C. W. Edg^erton, Baton Rouge, Louisiana. This culture was isolated 
from diseased cauliflower seedlings in the summer of 1012, so that it was a 
comparatively fresh culture when received here. 

Chenopodinm. — A culture was isolated during the summer of 1913 from ma- 
ture plants of Chenopodiuvi album growing along the border of the old herbaceous 
grounds back of the florieultural greenhouses. 

Clover. — A culture of Rhizoctonia from red-clover roots was received from 
Mr. E. A. Arzberger, Wooster, Ohio, March 3, 1913. The fungus was isolated 
by him from red -clover roots in the greenhouse in December, 1912. 

Coleus I. — This strain was obtained from coleus cuttings found damping off 
in the florieultural greenhouses, November, 1912. 

Coleus II. — A culture was isolated from coleus seedlings damping off in seed 
pans, October, 1913, in the florieultural greenhouses. 

Corn. — The strain from corn was obtained from Dr. J. J. Taubenhaus, New- 
ark, Delaware, in 1912. He stated that the fungus had been isolated from com 
seedlings that were damping off in the greenhouse. 

Cotton. — Three cultures of Rhizoctonia from cotton received from two 
sources at different times, were used in these experiments. The strain ' ' Cotton I ' ' 
was received from Dr. C. W. Edgerton, Baton Rouge, Louisiana, November 12, 
1912. This strain was cultured by him in September, 1911, from young diseased 
plants. The strain "Cotton II" was also received from Dr. Edgerton. This 
strain was cultured in February, 1912, from the same kind of material as the 
above. The third strain, ' ' Cotton III, ' ' was received from Dr. F. C. Wolf, 
Auburn, Alabama, December 12, 1912. The fungus was isolated from seedling 
cotton plants growing in the station greenhouse at Auburn. 

Dianthus. — Cultures of Rhizoctonia were isolated during July, 1913, from 
diseased plants of several species of Dianthus growing in the perennial garden. 
TTie strains cultured and used in the experiments were "D. barbatus N. P.," "D. 
liarbatus S. M.," "D. plumarius, " and "D. sequeri. " 

Eggplant. — Two strains of Rhizoctonia were isolated from eggplant : one, 
causing a fruit rot, was cultured August, 1912 ; the other was isolated from seed- 
lings damping off in flats in the vegetable-gardening greenhouse, July, 1913. 

GypsopMla repens.- — A culture of Rhizoctonia was isolated during July, 1913, 
from diseased GypsopMla plants in the perennial garden. 

Lavatera. — A culture was isolated in 1913 from seedlings of lavatera found 
damping oflf in pans in the florieultural greenhouses. 

Lettuce. — The strain from lettuce was obtained by Mr. Anderson in 1911, 
from Cornell University. 

Poinsettia. — Cultures were obtained from damping-off poinsettia cuttings 
found in the florieultural greenhouses, October, 1912. 

Potato. — Several strains from potato were used in these experiments. Two 
of these strains were obtained from scrapings of the hymenial layer of the Corti- 
cium stage. 

' ' Potato R.P.C. ' ' — A culture of this strain was isolated from fresh potato 
stems received from Dr. I. C. Jagger, Williamson, New York, September 2, 1912. 
This material contained the perfect stage, Corticium vagum B. & C. Pure cul- 
tures of Rhizoctonia were obtained from scrapings of the hymenial layer. 

"Potato R.P.I." — In response to a letter from Mr. Anderson, Dr. Geo. II. 
Pethybridge, Clifden county, Galway, Ireland, sent a small box of potato stems 
containing the perfect stage, Corticium vagum B. «& C. This material was sent by 
post, July 18, 1912, and received August 5. A pure culture of Rhizoctonia was 
obtained from scrapings of the gi'ay mycelium of the Corticium stage. 

' * Potato R.P.O. ' ' — A culture from potato was obtained by Mr. Anderson 
from Cornell University. The strain Avas old and grew very poorly on agar. 

' ' Potato R. Sol. ' ' — This strain, like the preceding one, was obtained by Mr. 
Anderson from Cornell University. It also grew very poorly on agar. 

Badish. — A culture of Rhizoctonia from radish was obtained from Cornell 
University, by Mr. Anderson, in 1911. This form was very old and probably had 
been in culture several years. It was lost in April, 1913. 



340 



Bulletin No. 189 



[June, 



Salvia. — The strain from salvia was isolated from cuttings which were found 
in the same bench with a number of other cuttings damping off, October, 1912. 

Sedtim. — A culture of Ehizoctonia from sedum was isolated from diseased 
plants found in the herbaceous grounds in July, 1913. 

Sugar Cane. — A culture of Ehizoctonia isolated from sugar cane was re- 
ceived from Dr. C. W. Edgerton, November 12, 1912. This culture was obtained 
in April, 1912. It was fresh and virulent. 

Thistle. — A culture of Ehizoctonia from thistle was obtained by Mr. Ander- 
son from Cornell University in 1911. 



The method of infecting the cuttings, seedlings, and young plants 
grown in flats and benches, was as follows : Small flats, varying in size 
with the experiment, were first soaked in a strong solution of formalin 
for several minutes and then allowed to dry. Steam-sterilized sand 

or soil and a soil culture of Rhi- 
zoctonia were then mixed to- 
gether in the flats and watered. 
After being tamped down, the 
flats were left standing for two 
days in order to allow the fun- 
gus to spread thru the soil. 
Later, the cuttings, seeds, or 
plants were put in the flats and 
placed in a chamber in the green- 
house where the moisture could 
1)6 controlled. Bottom heat was 
furnished. The temperature var- 
ied somewhat during the experi- 
ment, but the average was about 
60° F. When only individual 
plants in pots or in benches were 
to be infected, a portion of a cul- 
ture of Ehizoctonia two weeks 
old on green-bean plugs was 
placed in contact with the stem 
of each plant about one-half 
inch below the surface of the soil, 
where it would be protected from 
light and desiccation. 

In obtaining soil cultures of 
Rhizoctonia in large quantities. 
Mason jars with modified covers 
were found to be very suitable 
containers. A hole about one 
inch in diameter was cut in the 




Fig. 



17. — Soil Culture 
Ehizoctonia 



1916] Parasitic Ehizoctonias in America 341 

center of the cover, and a small tin tube about two inches long was in- 
serted and soldered in. This hole was plugged with cotton. (See 
Fig. 17.) A mixture of 200 grams of dry sand and 10 grams of corn 
meal was then placed in the jars and moistened with distilled water 
until the sand was wet thru. The jars and their contents were then 
sterilized for one hour at twenty pounds pressure in an autoclave, after 
which the sand was inoculated with a small piece of infected green- 
bean plug upon which Rhizoctonia was growing luxuriantly. In about 
a month the soil was permeated with the mycelium, and numerous 
brovN^n sclerotia of various sizes were formed. When smaller amounts 
of infected soil were needed, a 250-cc. flask was used. 

No plant was listed as diseased until a pure culture of Rhizoctonia 
had been isolated from it. Pure cultures were easily obtained by soak- 
ing small pieces of diseased parts in 1-1000 mercuric chlorid for two 
minutes and then placing them on green-bean agar. Rhizoctonia 
developed rapidly, and in twenty-four to forty-eight hours would 
spread out from the diseased parts. 

Experiments 1 and 1a : Inoculation of Carnation Cuttings with 
Various Strains of Rhizoctonia 

Rhizoctonia is the fungus most commonly found causing a damp- 
ing-off of carnation cuttings in the greenhouse. To determine whether 
any of the strains from sources other than carnation are able to attack 
carnation cuttings with the same ease as those from carnation, the fol- 
lowing experiment was carried out. Nine hundred carnation cuttings 
and 28 strains were used in 1913, and 1,725 cuttings and 34 strains 
in 1914. 

Sterilized flats (7x10 inches) were filled with sterilized sand; a 
250-cc. soil culture of Rhizoctonia was then added to each and the 
sand tamped down and watered. One flat was left uninoculated to 
serve as a check. After two days, thirty carnation cuttings (White 
Enchantress) were planted in each flat, January 2-3, 1913. The flats 
were then placed in the moist chamber. 

The inoculated cuttings began to die in about three weeks (Jan- 
uary 25), and continued dying until the healthy cuttings had rooted, 
when the experiment was discontinued (February 11) (Fig. 18). The 
results are given in Table 3. 

In most cases the cuttings inoculated with the various strains from 
carnation showed a soft, wet, progressive rot at the callus, which 
extended in many cases to the surface of the sand. This rot was very 
characteristic of the attacks of the carnation strains (Fig. 12). At 
other times the fungus attacked the cuttings just below the surface 
of the soil, forming lesions of various sizes at the leaf bases. Myce- 
lium and sclerotia were also formed along the stems and in practically 
all cases between the leaves just above the soil. 



342 



Bulletin is'o. IS!) 



[June, 



Table 3. 



-Susceptibility of Carnation Cuttings to Various Strains of 
Ehizoctonia: Experiments 1 and 1a 



Strain 



Date of 
isolation 



Number of plants 



Experiment 1: 1913 



Healthy Wilted Dead 



Experiment la: 1914 



Healthy Wilted Dead 



Alfalfa 

Alternanthera E.A.O. 
E.A.r. , 

Amaranthus , 

Aster 

Bean 

Beet 

Begonia 

Carnation E.K 

' ' E.O 



R.H 

R.S 

E.2 

" E.F 

" E.M.2 

" E.107 

" E.F.2 

Carrot 

Cauliflower 

Chenopodium 

Clover 

Coleus I 

" II 

Corn 

Cotton I 

" II 

" III 

Dianthus barbatus S.M. 
" N.P. 

" plnmarius 

' ' sequeri 

Eggplant I 

II 

Lavatera 

Lettuce 

Poinsettia 

Potato E.P.C 

" R.P.I 

" E.P.0 

" E.Sol 

Salvia 

Sedum 

Sugar cane 

Thistle 

Check 



1910 
1912 
1912 
1913 
1913 

1913 
1911 
1911 
1911 
1911 
1911 
1912 
1912 
1912 
1912 
1913 

1912 
1913 
1912 
1912 
1913 
1912 
1911 
1912 
1912 
1913 
1913 
1913 
1913 
1912 
1913 
1913 

1912 
1912 
1912 



1912 
1913 
1912 



10 


14 




3 




2 


2 


2 


3 2 





3 


1 


2 


3 



33 




5 


8 


7 


1 


) 














3 






3 


1 


2 


1 . . 




19 


11 


( 






6 





o^ 


i 





5 


2 


2. 









2 


2! 









2 


2, 


^ 3 





1 


3 


2t 


3 22 


9 


2 


3 


2. 


J 4 







4 


18 


! 


i 32 


2 








3( 


) 
33 

12 













3( 


1 



31 




3 








3( 


) 18 











3( 


) 4 
14 






2 

1 





14 


6 


1( 


) 3 

8 





1 


18 


12 


( 


) 34 





7 


1 ' 


2' 


3 23 





4 


2 


2- 






9 


4 


1' 






9 


7 


1' 






10 


6 


1- 






16 


11 




5 24 



2 



o 


3 


2'- 


t 34 


3 


8 


18 




i 24 


2 


4 


26 


( 


46 
47 


2 

1 



'This strain had been in culture for a number of years; the exact year of 
isolation is not known. 



1916] 



Parasitic Eiiizoctonias in America 



343 




Fig. 18. — Experiments 1 and 1a: Carnation Cuttings Infected with Ehizoc- 
TONiA Strains (1) Carnation R.K.; (2) Carnation R. 107; {S) Car- 
nation R.O.; (4) Carnation R.F. (.5) Begonia; (6) Coleus; (7) Poin- 
settia; (8) Salvia; (9) Cauliflower; (10) Thistle; (11) Lettuce; 
(12) Potato E.P.C; (13) Cotton; (14) Bean; (15) Potato R.P.O.; (16) 
Carrot 



344 Bulletin No. 189 [June, 

The percentage of infection was about the same with all the carna- 
tion strains except "Carnation R.O.," which appeared to have lost 
practically all power of attacking cuttings. This was one of the first 
strains isolated from carnation. Thus the age of the strain seemed 
to play an important role in its virulence, and for this reason the date 
of the original isolation of each strain is included in the table. 

The strains from alternanthera, coleus, salvia, and poinsettia, all 
cf which were isolated from diseased plants in the same cutting bench, 
l>roduced in some cases a soft wet rot of the carnation cuttings similar 
to that caused by the carnation strains. In the majority of cases, how- 
ever, these strains attacked the cuttings at the callus, forming large 
brown sclerotia which covered the whole callus and so prevented the 
formation of roots. Brown strands of the mycelium and sclerotia 
were formed on all parts of the cuttings underground and also be- 
tween the leaves. Occasionally, small lesions appeared at the leaf 
bases which were slightly under the surface of the sand. 

The two strains from alternanthera and the one from poinsettia 
killed about the same number of cuttings as the strains from carna- 
tion, while the one from coleus caused 100-percent infection and rotted 
the cuttings off faster than the strains from carnation. The percent- 
age of infection with the strain from salvia was very low. 

The strain from begonia produced a soft rot somewhat different 
from that produced by the carnation strains. It appeared on the stem 
at the surface of the soil and sometimes at the callus. The fungus 
formed a dense mass of mycelium which completely covered the sand 
beneath. Here again the virulence was greater than with the carna- 
tion strains, all the cuttings being killed and in a much shorter time. 

The strains from eggplant, lettuce, and thistle for the most part 
formed many sclerotia on the stems and in between the leaves of the 
cuttings, with only an occasional sclerotium at the callus. Small 
lesions were found to be abundant at the leaf bases and on the stems. 
These strains were very weak, especially those from lettuce and thistle, 
which had been in culture for a number of years. 

The cuttings infected with strains from cotton, cauliflower, and 
sugar cane rotted off at the surface of the soil ; the rot started as a 
lesion at this point and progressed very rapidly until the cutting was 
killed. Smaller lesions were produced on the stem underground. 
Sclerotia and the brown strands of the fungus could be found in 
abundance on the parts below the soil. The strains from cotton and 
cauliflower were very virulent; all the cuttings inoculated with them 
were killed one week before the cuttings inoculated with a soil culture 
of the carnation strains began to die off. 

The potato strains, as a rule, produced a large number of sclerotia 
and a dark brown mycelium below the soil and on the leaves. The 
percentage of infection was fairly high and uniform altho the average 
v/as below that of the carnation strains. 



1916] Parasitic Rhizoctonias in America 345 

The strains from alfalfa, bean, and carrot produced symptoms simi- 
lar to those from potato. A lar^e number of the cuttinj^s placed in 
the uninoculated sand wilted, but none became diseased. 

During the spring of 1914, beginning on March 7 and ending on 
April 7, the experiment was repeated, the only difference being that 
a number of additional strains were used and flats containing forty- 
eight cuttings instead of thirty. As will be seen in Table 3, the re- 
sults were confirmatory. The marked increase in the virulence of the 
lettuce strain may have been due in part to the influence of tempera- 
ture both on the strain and on the cuttings. 

Experiments 2 and 2a ; Inoculation of Young Carnation Plants 
WITH Various Strains of Rhizoctonia 

That the majority of strains can attack carnation cuttings was 
shown in Experiments 1 and la, where it appeared that the virulence 
of the strain did not depend on the host from which it was originally 
isolated, but in some cases did depend on the length of time since the 
culture was isolated. To determine whether rooted plants were as 
susceptible to these various strains of Rhizoctonia as were cuttings, 
further experiments were carried out : Experiment 2 in 1913, involv- 
ing about 400 young plants and 24 strains; and Experiment 2a in 
1914, in which about the same number of plants but only 13 strains 
were used. 

Carnation cuttings (White Enchantress) which had been placed in 
sterilized sand December 12, 1912, were planted February 12, 1913, 
in sterilized flats (9x12 inches) containing sterilized soil, fifteen plants 
in each flat. Plants failing to strike root were pulled out, leaving an 
unequal number in the various flats. The flats were inoculated on 
March 23 with 250-cc. soil cultures of Rhizoctonia, each flat with a 
different strain. They were then placed in a case in the greenhouse 
and left during April and May. 

Usually the carnation strains, as in the case of the cuttings (Ex- 
periments 1 and la), produced a soft, wet rot at the surface of the soil 
or just below. On other plants they caused small lesions of various 
sizes along the stems, killing the plants slowly. Sclerotia and brown 
strands of mycelium were as a rule present on plants which showed 
lesions and on others less badly diseased. 

Only an occasional plant in the flats infected with other strains 
than carnation developed a soft, wet rot. In the majority of cases 
where infection took place the strains produced lesions of various sizes 
on the stems at the surface of the soil or just below, slowly killing the 
plants (Fig. 13). As a rule, sclerotia and mycelium were also present 
on the stems of the infected plants. The plants in the check flat re- 
mained healthy. 



346 



Bulletin No. 189 



[June, 



The resistance of the rooted carnation plants to the fungus, as 
shown in Table 4, was much more marked than with the cuttings. In 
the few exceptions the fungus appeared able to infect the plants al- 
most as readily as it had the cuttings. 

In 1914 this experiment was essentially repeated. Thirty young car- 
nation plants (Rosette) were placed in each of a number of flats 
(12x18 inches). On April 26, after the plants were rooted, some of the 
old infected sand from the inoculated flats used in Experiment la was 
mixed with the soil in which the plants were growing. The experiment 
was continued until June 1. The results, which are presented in 
Table 4, were similar to those of Experiment 2. As in that experiment, 
the plants in the check flat remained healthy, with the exception of 
two that wilted and died from attacks of a Fusarium. 



Table 4. — Susceptibility op Young Rooted Carnation Plants to Various 
Strains op Ehizoctonia: Experiments 2 and 2a 







Number 


of plants 




Strain 


Exper 


iment 2: 1913 


Experiment 2a 


: 1914 




Total 


Healthy 


Dead 


Total Healthy 


Dead 


Alternanthera R.A.C 

R.A.r 

Amarantbns 


15 
15 

15 
14 

14 
13 
14 
15 
14 
15 

15 
15 
15 
15 
15 
14 

15 

i.5 
15 
14 
14 
15 

i.5 

14 
15 


12 

5 

14 
2 

i 

6 
2 

2 
4 

13 
9 
9 

2 

8 

10 

G 

13 

15 
7 
8 

10 

13 
12 
15 


3 

10 

i 

12 

13 
7 
12 
15 
12 
11 

2 

6 

6 

13 

7 
4 

9 

2 


7 
6 
5 

2 

(} 




30 
30 
30 

30 

30 

30 

30 
30 
30 

30 
30 
30 

30 
30 


18 
25 
20 

15 
j5 

io 

22 
23 
13 

12 
24 
19 

24 

28 


12 
5 


Beet 


10 


Begonia 




Carnation R.K 




" R.H 


15 


" R.S 

" R.2 




" R.F 




" R.F 


15 


R.M.2 

R.107 

R.F.2 

Carrot 


20 


Cauliflower 


8 


Coleus I 


7 


Cotton I 


17 


" II 


, , 


" III 




Dianthns barbatiis N.P 

Eafa'plant I 


18 
6 


Lavatera 


11 


Lettuce 




Potato R.P.C 

" R.P.T 

" R.P.O 

Salvia 


•• 


Seduni 


6 


Sucrar cane 




Thistle 


. . 


Check 




>; 


2» 


"Killed by Fusarium. 















1916] 



Parasitic Rhtzoctonias in America 



347 



Experiment 3: Inoculation of Old Carnation Plants in Pots 
WITH Various Strains of Rhizoctonia 

The resistance of young rooted carnation plants to the various 
strains of Rhizoctonia other than those from carnation was very 
marked in Experiments 2 and 2a. To determine whether or not old 
carnation plants were even more resistant, the following experiment 
was carried out, involving 90 plants and 18 strains. 

Carnation plants (White Enchantress and White Perfection) 
were brought in from the field and planted in pots, which were then 
placed in the bench. The plants were grown under the best possible 
cultural conditions and on November 27, 1912, when they had become 
firmly established, they were inoculated. Five plants of the same size 
were used for each test, one being left as a check. The other four were 
inoculated by placing a bit of infected green-bean plug near the stem 
about one-half inch below the surface of the ground. The stems of 
two plants of each test were slightly wounded before the plugs were 
placed by them. Observations were discontinued on March 27, four 
months later. The results are presented in Table 5. 

Only two plants inoculated by contact died during the course of 
the experiment, and both were killed by carnation strains. However, 
where the stem was slit, the various strains were in most cases able to 
infect and kill the plant. The check plants remained healtliy during 
tlie experiment. 



Table 5. — Susceptibility op Old Carnation Plants (in Pots) to Various 
Strains of Rhizoctonia: Experiment 3 



Strain 



Plants inoculated by 



Contact 



Slit 



Healthy Diseased Healthy Diseased Healthy Diseased 



Cheek plants 



Alternanthera R.A.F 


Carnation 


R.K 


" 




R.O 






R.H 

R.S 


J > 




R.2 


) > 


R.F ! 


} y 




R.M.2 


J J 




R.107 


Carrot 






Cotton 


II 

nt 




Eggpla 
Lettuce 


I 


tia 
R. 
R. 
R. 




Poinset 




Potato 


Sol 


} > 


p.o 


J f 


P.I 


Thistle 





2 





1 


1 







2 








2 







2 








2 







2 








2 







1 


1 





2 







1 


1 





2 







2 








2 







2 





1 


1 















2 







2 





2 










2 





1 


1 







2 








2 







2 








2 







2 








2 







2 








2 







'> 





1 


1 







2 








2 







2 








2 








348 



Bulletin No. ISO 



[June, 



Experiment 4: Inoculation of Young Carnation Plants with 
Isolated and with Eeisolated Strains of Rhizoctonia 

The object of Experiment 4 was to compare the virulence of various 
strains of Rhizoctonia when they were, inoculated on carnation plants 
for the first time, and after they had been inoculated on carnation 
and reisolated. Fifteen strains, taken at random, and about 300 plants 
were used. 

On December 12, 1912, a number of carnation cuttings were made 
and placed in sterilized sand. They were allowed to remain in the 
sand until well rooted. On March 22, when the plants were from 
four to six inches high and breaking nicely, they were placed in three- 
inch pots in sterilized soil. They were then inoculated by placing a 
bit of bean pod infected with Rhizoctonia near the stem just below the 
surface of the soil. Table 6 gives the results obtained. 

With seven strains the virulence of the reisolated fungus was 
slightly greater than that of the original isolation. With two it was 
slightly less. 

Table 6.- — Comparative Virulence of Isolated and Reisolated Strains of 
Ehizoctonia When Inoculated on Young Carnation Plants (in Pots) : 

Experiment 4 



Strain 



Original isolation Eeisolation 



Healthy Diseased Healthy Diseased 



Bean 

Carnation R.K.. 

' ' R.K. . 

' ' R.H. . 

" R.S... 

" R.2.. 
E.F. . 

" R.F.. 
R.M.2 

" R.107 
Cauliflower ... 

Cotton I 

" II 

Potato R.P.I. . 
Sugar cane . . . 
Check 



9 


1 


9 


6 


4 


1 
1 


h 


5 


2 


6 


4 


r> 


10 





7 


7 


3 


4 


4 


6 


7 


4 


G 


5 


10 





10 


9 


1 


7 


10 





10 


9 


1 


8 


10 





9 


10 







10 







10 








Experiment 5: Inoculation of Old Carnation Plants in the 
Bench with Various Strains of Rhizoctonia 

Experiment 5 was similar to the preceding experiment except that 
the carnation plants used were older and were grown in the bench in- 
stead of in pots, and that inoculations were made with only eight 
strains of Rhizoctonia, chosen at random. 



1016] 



Parasitic Ehi'/COctonias in America 



349 



On September 1, 1913, the soil in two five-foot sections in the green- 
house was sterilized, and twenty carnation plants from the field were 
placed in each section, four plants in a row. Four rows in each sec- 
tion were each inoculated with a different strain of Rhizoctonia, by 
means of pieces of infected bean plugs. The middle row in each sec- 
tion was left as a check. 

The plants began to die off at the end ol three weeks and con- 
tinued dying until the close of the experiment, October 31. They all 
died in a manner characteristic of stem rot. All the strains used 
proved to be virulent except the one from beet (see Table 7). The 
check plants remained healthy thruout the experiment. 



Table 7. — Susceptibility of Old Carnation Plants (in the Bench) to 
Various Strains of Ehizoctonia: Experiment 5 



Strain 


Healthy 


Diseased 


Beet 


3 

1 



1 


1 
1 

4 
4 


1 


Carnation E.107 


4 


Cauliflower 


3 


Cotton II 


4 


Dianthus barbatus 8,M 


3 


' ' plumarius 


4 


Eggplant I 


3 


Potato E. Sol 


3 


Check 





) ) 










The high mortality of the strains in this experiment was due, to a 
large extent, to the date of inoculation. The plants in the preceding 
experiments were inoculated either late in the fall or in the early 
spring, when the temperature in the greenhouse was low and normal 
and not influenced by outside conditions. The temperature in the 
house during September and October, when these plants were inocu- 
lated, is very high ; hence the virulence of the fungus was much greater. 
The effects of inoculating plants at various times of the year are 
clearly brought out in the next experiment. 



Experiment 6 : Inoculation of Carnation Plants with Ehizoc- 
tonia AT Different Temperatures 

During the season 1913-14 a number of sections containing carna- 
tions were reserved in the greenhouse, and at different times of the 
year the plants were inoculated with Rhizoctonia from carnation. 
This experiment was for the purpose of ascertaining the relative 
virulence of Rhizoctonia when inoculated on carnation plants at dif- 
ferent temperatures. 

Each section contained twenty plants, sixteen of which were in- 
oculated by placing infected bean plugs at the base of the stem. The 
remaining four plants served as checks. 



350 



Bulletin No. 189 



[June, 



Table 8. — Eelative Virulence of Ehizoctonia Inoculated on Carnation 
Plants at Different Temperatures: Experiment 6 





Date of 
inoculation 


Experiment 
discontinued 


Inoculated plants 
Healthy 1 Diseased 


Check 


plants 


Section 


Healthy 


Diseased 


143 


Sept. 1, 1913 


Oct. 1, 1913 


1 


15 


4 





140 


Oct. 1, 1913 


Nov. 1, 1913 


3 


13 


4 





139 


Nov. 1, 1913 


Jan. 1, 1914 


10 


6 


4 





138 


Dec. 1, 1913 


Feb. 1, 1914 


8 


8 


4 





137 


Jan. 1, 1914 


Mar. 1, 1914 


14 


2 


4 





134 


Feb. 1, 1914 


Apr. 1, 1914 


3 


13" 


4 





133 


Mar. 1, 1914 


May 1, 1914 


12 


4 


4 





132 


Apr. 1, 1914 


June 1, 1914 


9 


7 


4 





131 


May 1, 1914 


July 1, 1914 





16 


4 





130 


June 1, 1914 


July 1, 1914 


2 


14 


4 





128 


July 1, 1914 


July 23, 1914 


6 


10 


4 






"Ten plants found infected April 1 ; only three plants died during the months 
of February and March. 

As can be seen from Table 8, the death rate of the plants inocu- 
lated on September 1 and October 1 was almost 100 percent. This 
rate diminished very markedly when the plants were inoculated later 
in the season, increasing with the plants inoculated during the spring 
months until with those inoculated on May 1, it had again reached a 
high percentage. This condition prevailed during the summer months, 
showing very noticeably the influence of temperature on mortality. 

Experiment 7: Inoculation of Various Hosts (Seedlings) Other 
THAN Carnation with Various Strains of Rhizoctonia 

In the preceding experiments all the work was carried on with 
carnation plants of different ages. It was found that under certain 
conditions all the strains used could attack these plants, but that the 
resistance was somewhat increased when the plants Avere rooted. To 
determine whether the same results could be obtained with other 
plants, a number of further experiments were made. 

Small flats (8x10 inches) were disinfected and filled with a mix- 
ture of sterilized sand and soil suitable for germinating seed. In each 
flat a 250-ce. soil culture of one of the various strains used was thoroly 
mixed with the soil, and the whole allowed to stand for several days. 
The seeds, after a short soaking in formalin (1-150), were sown in the 
flats, thirty-one in all, care being taken not to plant them too closely. 
Nine different kinds of seedlings and 13 strains w^ere used in the ex- 
periment. The results obtained are given in Table 9. 

In the first group of the various hosts, clover proved to be more 
resistant than alfalfa, while the injury to corn roots was negligible. 
Of the different strains, the one from clover proved the most virulent, 
while the one from corn was the weakest (Fig. 19). 



1D16] 



Parasitic Rhizoctonias in America 



351 



Table 9. — Susceptibility op Various Plants (Seedlings) Other than Carna- 
tion TO Various Strains of Rhizoctonia: Experiment 7 



Group 1 



Strain 


On clover 


On alfalfa 


On corn 


Olover 


150 seeds 
Most of seedlings 
killed at germina- 
tion ; 6 came up ; 
5 infected below 
surface of ground, 
showing lesions ; 
1 healthy 


150 seeds 
All seeds attacked 
by fungus at ger- 
mination. Rhizoc- 
tonia present in 
seeds 


30 seeds 




Plants 4-6 inches 
high. Seed in all 
cases showed the 
presence of Rhi- 
zoetonia, but 
whether it would 
kill the whole 


Alfalfa 


About 15 percent 
damped off in typ- 
ical manner. Le- 
sions at surface of 
ground 


80 percent damped 
off. Others in va- 
rious stages of in- 
fection. 5 percent 
healthy 


])lant is a ques- 




tion. However, 
fungus is able to 
live in the roots 
of the corn. Cul- 
tures of Rhizoc- 
tonia were ob- 
tained from the 
s?eds 


Carnatiou R. 107 . . 


Only few plants 
infected. First 
leaves of a large 
number dead from 
effects of fungus 


70 percent damped 
off. Condition sim- 
ilar to that of 
plants inoculated 
with alfalfa strain 


Corn 


2 percent damped 
off. Rhizoctonia 
present on the 
roots of living 
plants, but did not 
seem virulent 


8 percent damped 
off. Remaining 
plants healthy 









Group 2 



Strain 


On lettuce 


On eggplant 


On cabbage 


Lettuce 


150 seeds 
90 percent damped 
off. Lesions on 
stem at surface 
of ground. Leaves 
also attacked, 
causing a rot 


150 seeds 
2 percent damped 
off. Lesions at 
surface of ground. 
Typical 


150 seeds 


Eggplant I 


75 percent damped 
off. Lesions typi- 
cal, like lettuce 


3-4 percent damped 
off. Typical 




Thistle 


60 percent damped 
off. Lesions typi- 
cal, like those on 
plants inoculated 
with eggplant 
strain. Action of 
fungus slower but 
virulent 


5 percent damped 
off. Small circular 
lesions present. 
Typical 








Carnation R.F 


60 percent damped 
off. Like thistle; 
slower in effect, 
but still virulent 


All healthy 


-10 percent infected. 
Lesions in form 
of a collar 
around stem at 
surface of ground 


Cauliflower 


3 percent damped 
off. Typical le- 
sions 




Only 3 plants 
healthy. Seedlings 
attacked at ger- 
mination 



352 



Bulletin No. 189 



[June, 



Table 9. — Concluded 



Group 3 



Strain 


On radish 


On turnip 


On beet 


Radish 


150 seeds 
1 percent infected 
at base of stems. 
Several completely 
rotted 


150 seeds 
Seedlings attacked 
at germination. 
Only 2 healthy 
plants 


100 seeds 






Potato R.P.C. . . . 


15 percent infected 
at base of stems 
where root begins. 
Small wounds like 
potato scab due 
to Rhizoctonia 




50 percent damped 
off. Some rotted 
off at the ground 


Carrot 


Seedlings attacked 
at germination. 
Only 3 healthy 
plants 


50 percent infected. 
All showed collar 
rot. Some rotted 
off 








Carnation R.F. . . 


50 percent infected. 
Lesions at base of 
stems. Few rotted 
off 




98 percent damped 
off. Showed collar 
rot. Typical 




Fig. 19. — Experiment 7: Upper Row: Alfalfa Seedlings Infected with 
Rhizoctonia Strains (1) Clover; (2) Alfalfa; (3) Carnation R. 107! 
(4) Corn. Lower Row: Lettuce Seedlings Infected with Rhizoctonia Strains 
(1) Lettuce; (2) Eggplant I; (3) Thistle; (4) Carnation R.F. 



Of the seedlings in the second group, lettuce and cabbage were 
quite susceptible ; eggplant seedlings were very resistant. The strain 
from cauliflower, altho it caused only a slight damping-off of lettuce 



]916] Parasitic Ehizoctonias in Amkrica 353 

seedlings, produced practically 100-percent infection in the case of 
cabbage seedlings (Fig. 19). 

In the third group, beet, radish, and turnip seedlings proved very- 
susceptible to damping-off of Rhizoctonia. It is rather interesting to 
observe that while the strain from radish was able to cause only 
1-percent infection of radish seedlings, it caused almost 100-percent 
infection of turnip seedlings. 

Taking the experiment as a whole, it is seen that a great variation 
exists in susceptibility of seedlings and in virulence of strains. It is 
clear that under certain conditions all the strains can attack a given 
host with about the same virulence. 

Experiment 8: Inoculation of Various Hosts (Old) Other than 
Carnation with Various Strains op Ehizoctonia 

In Experiment 8 the preceding experiment was carried one step 
farther, older plants being used rather than seedlings. A number of 
plants were taken from flats while small and transplanted to four-inch 
pots, where they were allowed to grow for about two months. The 
soil in these pots was not sterilized. Each plant, with the exception of 
the check plants, was inoculated by placing an infected bean plug in 
contact with it just below the surface of the soil. Four kinds of 
plants, 50 of each, and 12 strains were employed. Tho, observations 
from this experiment are recorded in Table 10. 

In Group 1, the tomato plants proved resistant to the attacks of 
the various strains, with the exception of the one from carnation, which 
produced a slight infection on two plants. In the case of the cabbage 
plants, the strains from cotton and from cauliflower exhibited a marked 
specialization, producing 50- and 90-percent infection, respectively, on 
these plants, while on tomato plants they produced no infection what- 
ever. Cabbage was the only host in the experiment susceptible to all 
the sti'ains with which it was inoculated. 

The carnation strains in Groups 2 and 3 also proved more virulent 
than the other strains, producing 50-percent infection on lettuce and 
] 00-percent infection on beet (Fig. 9). Of the other strains, eggplant 
alone was able to attack the plants, producing a slight infection on 
two lettuce plants. 

Experiment 9: Inoculation of Various Hosts (Cuttings, Seed- 
lings, AND Larger Plants) with Various Strains of Rhizoctonia 

The kinds of plants used in the foregoing experiments were some- 
what limited. Increased facilities being at hand in the spring of 1914, 
a more extensive series of inoculations was made with cuttings, seed- 
lings, and larger plants of various kinds. In all, about 350 cuttings, 
3,000 seedlings, and 300 larger plants were inoculated. Thirty-two 
strains of Rhizoctonia were used. 



354 



Bulletin No. 189 



[June, 





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1916] Parasitic Ehizoctonias in America 35S 

Flats (9x12 inches) were infected as in Experiment 7, and a vary- 
ing number of cuttings, seeds, and plants placed in them on March 7, 
1914. Pure cultures from the diseased plants in each flat were made, 
and Rhizoctonia was isolated in each case. Following, the results of 
the experiment are taken up in detail. 

" Alternanthera B.A.C." on Alternanihcra. — -JS ciitthigs. On March 18 all 
were dead. The infection \^as first noticed as a small, bi'own lesion on one side 
at the surface of the ground; later the lesion girdled the whole .stem. The fun- 
gus also attacked the cut surface of the cutting, causing a lesion and in some 
instances a slow, wet rot. The mycelium, which grew very profusely, attacked 
the leaves, producing a characteristic rot. 

"Alternanthera E.A.F." on Alternanthera. — 48 cuttings. The experiment 
was carried out exactly like the above and produced the same results. 

"Alternanthera R.A.F." on Gernanium. — 48 cuttings. These were planted 
March 20 in the infected flat in which alternanthera cuttings had died. By 
May 2, 42 of them Avere rotted while 6 were rooted and healthy. 

" Amaranthus" on Amaranihus salicifolius. — 100 seeds. Seeds germinated 
March 2.3, and by April 1 all the plants in the flat damped off in a character- 
istic manner. 

"Aster" on Aster. — 100 seeds. Seeds germinated March 18 and a few be- 
gan immediately to damp off. By April 1, 29 percent had died, while the others 
remained healthy. 

"Bean" on Bean.- — ,S0 ?eeds. Seeds germinated March 19, and after two 
months only .5 percent were killed by the fungus. 

"Beet" on Beet. — 100 feeds. Seeds germinated March 19 and began to 
damp off. About 25 percent damped off and later about 25 percent more be- 
came scabby because of the formation of small, depres-scd lesions. Injury here 
was similar to the infection of beet by the strains from carnation. 

"Carnation" on Bean. — 50 plants. On May 8, bean plants about three 
inches high were transplanted from flats to infected sections (Nos. 157 and 
173). The jdants took hold readily, and after about two weeks began to show 
signs of infection. The disease progressed rather slowly; most of the plants- 
produced a few pods before they were killed by the fungus. When pulled up. 
May 19, every one was diseased or dead (Fig. 8). A detailed description of 
four typically infected bean plants follows. It will be seen that it corresponds 
in most details to the descriptions given by Barrus,' Fulton,^^ and Hedgcock"" 

Plant No. 1: Three distinct lesions were present, one directly 
above the other on the stem. Lesions were oval in shape with a reddish 
brown band surrounding a lighter colored sunken area. Evidences were 
present of young lesions over the eiitire stem and larger roots under- 
ground. The wounds extended beneath the cortical layer to the woody 
tissue. 

Plant No. 2: Eoots were infected at the joint of their union with 
the main stem. The lateral root Avas very badly infected and rotted off 
entirely. The lesions on the smaller roots were small, depressed, and of 
a reddish brown color. 

Plant No. 3 : A large, reddish brown lesion extended from the sur- 
face of ground downward 2.5 centimeters. Spots were sunken and ex- 
tended thru the cortex to woody tissue beneath. Two small sunken areas 
of a reddish brown color were present on the stem one inch above the sur- 
face of the ground. 

Plant No. 4: A large, depressed, reddish brown area extended from 
the surface of the ground downward 2.5 to 3 centimeters, almost encircling 
the stem. Cortical tissue rotted away exposing the woody tissue beneath. 

"Carnation" on Beet. — 30 plants. On May 8, young beet plants were trans- 
planted to a section (No. 158) infected with Rhizoctonia from carnation. By 



356 Bulletin No. 189 [June, 

May 20 they all showed some scab. A number were infected at the crown, where 
a large number of leaves were completely cut off at the base by the fungus. Sev- 
eral beets had depressed lesions which extended deep into the tissues. 

"Carnation" on Callage.— 25 plants. On May 8, young cabbage plants 
were transferred from flats to a section (No. 163) in the greenhouse infected 
with a soil culture of Ehizoctonia from carnation. Some of these plants grew 
to maturity, but when they were pulled up. May 21, the stems and roots were cov- 
ered with black, depressed lesions (Fig. 11). Ninety percent of the plants set in 
the bench were infected in this way. Where the leaves touched the soil the fun- 
gus caused a slow, wet rot. 

"Carnation" on Carrot. — 50 plants. Carrot plants were transferred on 
May 8 from flats to an infected section (No. 158) in the greenhouse. By May 
21 only a few had rotted. The rot started at the crown, where the petioles were 
attacked, and worked down into the tissues of the root and up into the leaves. 
The rot from the crown goes into the interior of the root, and thus the root does 
not show any signs of rot on the outside for some time. Occasionally lesions 
were found on the sides of the carrots and on the larger roots where they branched 
from the fleshy part. 

"Carnation" on Corn. — 10 seedlings. Corn seedlings about 8 inches tall 
were transplanted on May 8 from flats to an infected section (No. 153) in the 
greenhouse. The plants grew to maturity. When pulled up, only small lesions 
were to be found on the roots. These were only slightly depressed and did not 
retard the growth of the plant. 

"Carnation" on Eggplant. — 25 plants. On May 8, eggplants were trans- 
ferred to an infected section in the greenhouse (No. 170). The plants reached 
maturity with no loss. When they were pulled up, no infection was to be found. 
"Carnation" on Lettuce. — 60 plants. On March 16, lettuce plants were 
transferred to an infected section (No. 153). By March 24, 16 percent of the 
plants were killed. No more loss occurred and the jjlants were cut on April 21. 
"Carnation E. 107" on Callage. — 100 seeds. Seeds germinated March 19 
and began to damp off immediately. By May 21 those which did not damp off 
Mere infected in various ways. Some had constrictions just at the surface of the 
soil; others had definite lesions along the stem and larger roots. Where the plants 
were crowded, spots of various sizes were formed on the lower leaves which touched 
the soil. 

"Carnation E.M.2" on Carrot. — 150 seeds. Seeds germinated March 18. 
When the experiment was discontinued. May 21, only 10 percent of the carrots 
were infected at the crown. One showed a constriction which was quite marked. 

"Carnation B.F." on Beet. — 100 seeds. Seeds germinated March 16 and 
began to damp off immediately, so that by March 24, 40 percent of the plants 
were dead. The remainder, when examined on May 21, were all more or less 
scabby. Some were rotted at the crown. 

"Carnation B.F.2" on Bean. — 30 seeds. Seeds germinated March 19. When 
the experiment was discontinued, May 8, but slight infection could be noticed. 

"Carrot" on Carrot. — 150 seeds. Seeds germinated March 16. By May 21 
only a few of the carrots were infected. An occasional plant showed crown rot, 
which was especially noticeable at the base of the leaves. 

"Cauliflower" on Callage. — 100 seeds. Seeds germinated March 13. A few 
f-eedlings began to damp off March 14 and by May 21 most of the plants were 
infected. Lesions could be found on the stems, occasionally one girdling the whole 
stem and forming a sort of constriction as the plant developed. A number of 
spots varying in size could also be found on the lower leaves which touched the 
soil. 

" Chenopodium" on Alfalfa. — 100 seeds. Seeds germinated March 13. Two 
weeks later 60 percent of the seedlings had damped off in a characteristic manner. 

"Clover" on Clover. — 150 seeds. Seeds germinated March 12 and began 
to damp off slowly. By March 21, however, the plants had reached sufficient 
size so that no more damping-off occurred. In all about 10 percent of the seed- 
lings were diseased. 



1916] Parasitic Ehizoctonias in America 357 

"Coleiis I" on Coleus. — 100 seeds. The f-eeds were all killed by the fun- 
gus as they were germinating. 

''Coleus I" on Coleus. — 48 cuttings. By March 18 all the cuttings had 
rotted off. Infection began as small spots at the surface of the ground or at 
the callus. Underground lesions of all sizes were produced, from small spots to 
places where the whole stem was girdled. The leaves of the cuttings were over- 
run with mycelium, the fungus in many cases rotting them off. 

'^Coleus II" on Chrysanthemum. — 48 cuttings. The old infected flat in which 
the coleus cuttings had rotted oft" was planted to chrysanthemum cuttings March 
20. By March 27 all of them had rotted oft" at the surface of the ground. In 
some a soft, wet rot was produced. 

''Coleus 11" on Coleus. — 100 seeds. Seeds germinated March 24 and began 
to damp off slowly. By May 21 only 30 percent of the plants were still healthy. 

"Coleus II" on Coleus. — 48 cuttings. All cuttings rotted off as with "Coleus 
I." The red-colored cuttings rotted oft' faster and were much more susceptible 
than those of the green variety. 

"Corn" on Corn. — 50 seeds. Seeds germinated March 17. The plants grew 
to maturity. When pulled up, no signs of infection were noticed. 

"Cotton I" on Cotton. — 50 seeds. The fungus caused a rotting of the seeds 
as they germinated. 

"Cotton III" on Cotton. — 50 seeds. Results same as preceding. 

"Dianthus barbat^is S.M." on Dianthus barbatvs (Sweet William). — 100 
seeds. Seeds germinated March 19 and began to damp off immediately. By May 

22, 50 percent of the seedlings were diseased. 

"Dianthus barbatus N. P." on Dianthus barbatus (Sweet William). — 100 
seeds. Eesults same as preceding. 

"Dianthus plumarms" on Dianthus plumarius. — 100 seeds. Seeds germinated 
March 14. By May 22, 80 percent of the plants had damped off. 

"Dianthus seqneri" on Dianthus sequeri. — 100 seeds. Seeds germinated 
March 18 and began to damp oft' immediately. By May 22 only about 25 percent 
were still healthy. 

"Eggplant I" on Eggplant. — 150 seeds. Seeds germinated March 23. By 
May 8 only 3 to 4 percent of the plants had damped off. 

"Eggplant II" on Eggplant. — 150 seeds. Seeds germinated March 23. The 
fungus caused a rot of the seeds at germination. 

" Lavatera" on Lavatera trimestris. — 100 seeds. Seeds germinated March 
12. By May 22 about 25 percent of the seedlings had damped off (Fig. 14). 
On the remainder, lesions of various sizes were present, which in some cases girdled 
the stem just below the surface of the soil and formed a collar, or constriction. 

"Lettuce" on Lettuce. — 125 seeds. Seeds germinated March 13. By April 
1 all the young plants had damped off. 

" Poinsettia" on Euphorbia variegata. — 100 seeds. Seeds germinated March 

23. By May 22, 6 percent of the plants had damped oft'. 

"Salvia" on Salvia splendens. — 100 seeds. Seeds germinated March 23. By 
May 8, 6 percent of the seedlings had damped off. By May 21, 4 of the plants 
were infected. Lesions extending into the woody tissues were present on the stem. 

"Salvia" on Salvia splendens. — 48 cuttings. These cuttings rotted off very 
rapidly. Wherever the leaves touched the soil, they were rotted also. By April 
7, 41 cuttings were diseased and 7 were rooted and healthy. 

"Sugar Cane" on Amaranthus salicifolius. — 100 seeds. Seeds germinated 
March 23. On May 21 all the plants were perfectly healthy. No infection was 
present. 

"Thistle" on Clover.— 100 seeds. Seeds germinated March 13. On May 21 
all the plants were healthy. 

Additional Inoculations. — On April 1 six flats of infected soil used in the 
inoculation experiments with carnation cuttings were mixed with soil in larger 
Hats and four hills of potatoes were planted in each. The six flats represented the 



358 Bulletin No. 189 [June, 

six strains " Alternanthera E.A.F.," "Carnation R.F.," "Cauliflower," "Let- 
tuce," "Cotton," and "Dianthus barbatus." Only one or two potato sprouts 
came up from each hill and these were weak and spindling. After the tempera- 
ture became too high in the greenhouse, the flats were placed outside, so that the 
plants would develop further and produce tubers. The strains killed some of the 
young sprouts and dwarfed the others, showing that they were able to attack the 
potato i^lant. 

Here, as in the preceding experiments, the death rate of the vari- 
ous plants was quite variable. These differences appear to be due to 
the virulence of the fungus, to the susceptibility of the plant, or to a 
combination of factors. 

Experiment 10 : Inoculation of Various Hosts in the Field 
WITH Various Strains of Rhizoctonia 

All the inoculation experiments reported so far were conducted in 
the greenhouse. In the summer of 1914 a fourth of an acre of land was 
divided into three parts, separated by six-foot strips of ground. Sec- 
tion 1 was inoculated on May 20 with twenty cubic feet of infected soil 
taken from the inoculated benches in the greenhouse. The soil was 
spread upon the section, worked under, and watered for several days. 
Section 2 was left as a check. In Section 3 small bits of pure cultures 
of various strains of Rhizoctonia were added with the seeds and plants. 
The seeds were planted May 20, and the young plants were put in 
June 16. Altho the drouth of the summer interfered considerably, 
the results obtained were sufficient to show that RJiizoctonia Solani 
was active under field conditions as well as in the greenhouse. 

No infection occurred in the first two sections. In Section 3 in- 
fection was quite marked in a number of cases, especially on cotton, 
potato, and several greenhouse plants. Where the strain ' ' Cotton I ' ' 
was added to the cotton seeds, 100-percent infection occurred. In the 
case of potato, to which ' ' Carnation R.F.2 ' ' was added, a marked dif- 
ference was noticed, the plants in this section being dwarfed and 
spindling, while in the first two sections they were bushy and strong. 
The difference in the yield was as marked as the difference in growth 
of the plants. All the coleus plants infected with ' ' Coleus I ' ' were 
killed within two weeks after being set out. The same results were 
obtained from inoculating salvia plants with the strain from salvia. 

DISCUSSION OF INOCULATION EXPERIMENTS 

In Table 11 are brought together, in tabular form, the results of 
all the inoculation experiments, with the exception of No. 4, which 
was carried on primarily to test the comparative virulence of isolated 
and reisolatcd strains of Rhizoctonia. The thing that stands out at 
first glance is the great variation in the mortality of the plants when 
inoculated with strains from the same host and when inoculated with 
strains from other sources. 



1916] Parasitic Rhizoctonias in America 359 

When carnation cuttings were infected, the strains used, with but 
two exceptions, whether from carnation or from other hosts, were 
able to cause more or less loss, the mortality of the cuttings ranging 
in either instance from to 100 percent. Again, the same strains 
varied in virulence from one year to another, in most cases decreas- 
ing in virulence with age. When cuttings other than carnation were 
used, the results were the same. 

When young rooted carnation plants were inoculated, the percent- 
age of loss was much less than with cuttings. Here, however, the car- 
nation strains seemed to be slightly more virulent than those from 
other sources, altho there was still a great difference in the strains 
fiom carnation themselves. Only one of the strains from other sources 
was unaljlc to attack young rooted carnation plants. 

On old carnation plants in the greenhouse which were inoculated 
by contact, even the carnation strains did not cause a high percentage 
of infection. However, when plants growing under these same condi- 
tions were slightly wounded and then inoculated, the percentage of 
loss was very high in nearly all the strains studied. When conditions 
(temperature and moisture) were favorable to the fungus, most of the 
strains studied were able to infect carnation plants as readily as the 
carnation strains themselves. 

In the majority of cases all strains were able to cause damping-off 
of various seedlings. There was a great difference in the virulence of 
strains when inoculated on the same host from which they had been 
isolated and when inoculated on other hosts. Only occasionally was 
there any indication of marked specialization, and in no case was such 
indication corroborated in succeeding experiments. 

In older plants, a marked difference in susceptibility was found in 
the different species. As a rule, the root crops were highly susceptible 
to attacks of Rhizoctonia. Among these, beet appeared to be the most 
susceptible. Tomato and eggplant showed a very marked resistance 
to Rhizoctonia, and this was true to some extent of the potato also, 
altho under certain conditions it was quite susceptible. This varia- 
bility of resistance held true for most of the vegetable and field crops 
other than root crops. Under ordinary conditions, the majority of 
floricultural plants were not subject to attacks of Rhizoctonia, altho 
the mycelium of this fungus was known to be present in the soil or 
even on the plant itself. 

From the fact that all the strains studied showed the ability to 
attack the same species of plant and produce the same characteristic 
symptoms, it seems clear that they can be included under one form, 
li. Solani. These experiments show further that the virulence of 
R. Solani is very variable, as is also the degree of resistance of the vari- 
ous host plants, both depending on a number of varying factors. 



360 



Bulletin No. 189 



[June, 



Table 11. — Summary of Inoculation Experiments 





Original 1 


Date of 






Per- 


Strain 


date of 


inoculation 


Host 


Condition 


centage 




isolation 


experiment 






of loss* 


Alfalfa 


1910 


1913 
1913 


Alfalfa 
Cabbage 


Seedlings 
Plants 


95 




20 






1913 


Carnation 


Cuttings 


38 






1913 


Clover ■ 


Seedlings 


15 






1913 


Corn 


J 7 









1913 


Tomato 


Plants 





Alternanthera R.A.C. 


1912 


1914 


Alternanthera 


Cuttings 


100 






1913 


Carnation 


) 7 


92 






1914 


y > 


t) 


96 






1913 


) ) 


Young plants 


20 


Alteruanthera E.A.F. 


1912 


1914 


Alternanthera 


Cuttings 


100 






1913 


Carnation 


> 7 


90 






1914 


> ) 


}} 


100 






1913 


7 > 


Young plants 


66 






1914 


! ) 


77 *J) 


40 






1913 


7 ) 


Old plants 









1913 


) } 


(wonnded) 


50 






1914 


Geranium 


Cuttings 


87 


Amaranthiis 


1913 


1914 


Amaranthus 












salicifolius 


Seedlings 


100 






1914 


Carnation 


Cuttings 


100 






1914 


> > 


Young plants 


16 


Aster 


1913 


1914 
1914 


Aster 
Carnation 


Seedlings 
Cuttings 


29 




23 


Bean 




1914 
1913 


Bean 
Carnation 


Seedlings 
Cuttings 


5 




65 






1914 


) 7 


7 7 


100 


Beet 


1913 


1914 


Beet 


Seedlings 
Cuttings 


50 






1914 


Carnation 


IDO 






1914 


7 7 


Young plants 


33 






1913 


7 7 


Old plants 


25 


Begonia 


1911 


1913 


7 7 


Cuttings 
Young plants 


100 






1913 


7 7 


6 


Carnation R.K 


1911 


1913 


7 7 


Cuttings 


90 






1913 


7 7 


Young plants 


85 






1913 


7 7 


Old plants 









1913 


7 7 


(wounded) 


100 


Carnation R.O 


1911 


1913 


7 7 


Cuttings 









1913 


7 7 


Old plants 









1913 


7 7 


> ) 7 7 

(Avounded) 


100 


Carnation R.H 


1911 


1913 


7 7 


Cuttings 


80 






1914 


7 7 


> 7 


100 






1914 


7 7 


Young plants 


50 






1913 


7 7 


Old plants 









1913 


} ) 


(wounded) 


100 


Carnation R.S 


1911 


1913 


7 7 


Cuttings 


82 






1913 


} 7 


Young plants 


93 






1913 


7 7 


Old 


50 






1913 


7 7 


(wounded) 


100 



'In Experiments 
percentage of loss. 



1 and la the loss from plants wilted is not included in the 



]0J6] 



Tarasitic Rhizoctonias in America 



361 



Table 11. — Continued 





Original 


Date of 






Per- 


Strain 


date of 


inoculation 


Host 


Condition 


centage 




isolation 


experiment 
1913 


Carnation 




of loss" 


Carnation R.2 


1912 


Cuttings 


100 






1913 


7 » 


Young plant' 


54 






1913 


} J 


Old plants 


50 






1913 


} ! 


> ) } > 
(wounded) 


100 


Carnation R.r 


1912 


1913 


Beet 


Seedlings 


98 






1914 


) ) 


) > 


40 






1913 


Cabbage 


) 7 


40 






1913 


Carnation 


Cuttings 


100 






1914 


> > 


) ) 


94 






1913 


J !■ 


Young plants 


85 






1913 


» » 


) ) } } 


100 






1914 


' ' 


) ) ) J 


50 






1913 


' ' 


Old plants 









1913 


7 ) 


(wounded) 


100 






1913 


Eggplant 


Seedlings 









1913 


Lettuce 


} > 


fiO 






1913 


) ) 


Plants 


50 






1913 


Radish 


Seedlings 


50 


Carnation R.M.ii .... 


1912 


1913 


Carnation 


Cuttings 


96 






1914 


; > 


J > 


43 






1913 


> } 


Young plants 


85 






1913 


' ' 


Old plants 









1913 


J ; 


> } 5 J 

(wounded) 


50 






1914 


Carrot 


Seedlings 


10 


Carnation R.107 


1912 


1913 


Alfalfa 


J 5 


70 






1913 


Beet 


Plants 


100 






1914 


Cabbage 


Seedlings 


75 






1913 


Carnation 


Cuttings 


92 






1914 


" 


J J 


91 






1913 


> J 


Young plants 


73 






1913 


) ) 


Old plants 









1913 


> J 


7 ) ) J 

(wounded) 


100 






1913 


J ' 


Old plants 


100 






1913 


Clover 


Seedlings 


5 






1913 


Corn 


J ) 





Carnation R.F.2 


1913 


1914 


Bean 


J J 


3 






1914 


Carnation 


Cuttings 


100 






1914 


J > 


Young plants 


66 


Carnation R.121-5. . . 


1912 


1913 


Cabbage 


Plants 


70 






1913 


Tomato 


J > 


20 


Carnation (Sections 












157 and 












173) 




1914 


Bean 


>> 


98 


Carnation (Section 












158) 




1914 


Beet 


J } 


95 


( " 163) 




1914 


Cabbage 


J } 


90 


( " 158) 




1914 


Carrot 


) > 


10 


( " 153) 
( " 170) 




1914 


Corn 


Seedlings 







1914 


Eggplant 


Plants 





( " 153) 




1914 


Lettuce 


f f 


16 



"See footnote, page 360. 



362 



BULLE-TIN No. 189 



[June, 



Table 11. — Continued 





Original 


Date of 






Per- 


Strain 


date of 


Inoculation 


Host 


Condition 


centage 




isolation 


experiment 






of loss" 


Carrot 




1913 
1913 


Beet 
Carnation 


Plants 
Cuttings 







66 






1914 


) ; 


> > 


30 






1913 


) } 


Young plants 


13 






1913 


> > 


Old plants 









1913 


> > 


(wounded) 









1914 


Carrot 


Seedlings 


5 






1913 


Radish 


} ; 


98 






1913 


Turnip 


> f 


50 


Cauliflower 


1912 


1913 


Cabbage 


) } 


98 






1914 


J ) 


} ) 


97 






1913 


) ) 


Plants 


90 






1913 


Carnation 


Cuttings 


100 






1914 


> } 


} J 


100 






1913 


f ) 


Young plants 


40 






1914 


) > 


> f .' > 


26 






1913 


> } 


Old plants 


75 






1913 


Lettuce 


Seedlings 


3 






1913 


Tomato 


Plants 





Chenopodium 


1913 


1914 


Alfalfa 


Seedlings 


60 






1914 


Carnation 


Cuttings 


31 


Clover 


1912 


1913 
1914 


Alfalfa 
Carnation 


Seedlings 
Cuttings 


100 




75 






1913 


Clover 


Seedlings 


99 






1914 


J > 


> } 


10 






1913 


Corn 


J i 





Coleus I 


1912 


1913 
1914 


Carnation 


Cuttings 


100 




100 






1913 


} } 


Young plants 


40 






1914 


) ) 


>j >j 


23 






1914 


Coleus 


Seedlings 


100 






1914 


J } 


Cuttings 


100 


Coleus II 


1913 


1914 
1914 


Carnation 
Chrysanthemum 




100 




100 






1914 


Coleus 


Seedlings 


70 






1914 


> } 


Cuttings 


100 


Corn 


1912 


1913 
1914 


Alfalfa 
Carnation 


Seedlings 
Cuttings 


8 




51 






1913 


Clover 


Seedlings 


2 






1913 


Corn 


J > 









1914 


> > 


) > 





Cotton I 


1911 


1913 
1913 


Cabbage 
Carnation 


Plants 
Cuttings 


50 




100 






1914 


} ) 


) ) 


62 






1913 


> > 


Young plants 


87 






1914 


> > 


>) >> 


56 






1914 


Cotton 


Seedlings 


100 






1913 


Tomato 


Plants 





Cotton II 


1912 


1913 


Carnation 


Cuttings 


100 






1914 


> J 


> > 


91 






1913 


)) 


Young plants 


46 






1913 


J > 


Old plants 









1913 


> ) 


(wounded) 


50 






1913 


> > 


Old plants 


100 


Cotton HI 


1912 


1914 


> > 


Cuttings 


70 



"See footnote, page 360. 



1D16] 



Parasitic Ehizoctonias in America 



363 



Table 11. — Continued 





Original 


Date of 






Per- 


Strain 


date of 


inoculation 


Host 


Condition 


centage 




isolation 


experiment 






of loss" 


rintton III 


1912 


1913 


Carnation 


Young plants 
Seedlings 


28 


V^Wl'l'v'A-L J. J.-1- • •••••• 




1914 


Cotton 


100 


Dianthus barbatus 












S.M 


1913 


1914 


Carnation 


Cuttings 


98 






1913 


J > 


Old plants 


75 






1914 


Dianthus 












barbatus 


Seedlings 


50 


Diauthusbaibatus N.P. 


1913 


1914 


Carnation 


Cuttings 


100 






1914 


) ) 


Young plants 


60 


^ 




1914 


Dianthus 












barbatus 


Seedlings 


50 


Dianthus plumariuy. . 


1913 


1914 


Carnation 


Cuttings 


100 






1913 


> ) 


Old plants 


100 






1914 


Dianthus 












plumarius 


Seedlings 


80 


Dianthus sequeri 


1913 


1914 
1914 


Carnation 
Dianthus 


Cuttings 


100 








sequeri 


Seedlings 


75 


Effs^nlant I 


1912 


1913 


Carnation 


Cuttings 


42 


o&lr-'*^ ^ 




1914 


) ) 


93 






1913 


) > 


Young plants 


60 






1914 


1 > 


) > > > 


20 






1913 


J > 


Old plants 









1913 


J } 


(wounded) 


100 






1913 


} } 


Old plants 


75 






1913 


Eggplant 


Seedlings 


3 






1914 


}> 


) > 


4 






1913 


Lettuce 


} y 


75 






1913 


> ) 


Plants 


20 


Eggplant II 


1913 


1914 


Carnation 


Cuttings 


83 






1914 


Eggplant 


Seedlings 


100 


Lavatera 


1913 


1914 


Carnation 


Cuttings 


98 






1914 


J ) 


Young plants- 


36 






1914 


Lavatera 












trimestris 


Seedlings 


95 


Lettuce 




1913 
1914 


Carnation 


Cuttings 







34 






1913 


) > 


Young plants 


13 






1913 


) » 


Old plants 









1913 


7 ) 


(wounded) 


100 






1913 


Eggplant 


Seedlings 


2 






1913 


Lettuce 


) J 


90 






1914 


)) 


> ) 


100 






1913 


? > 


Plants 





Poinsettia 


1912 


1913 


Carnation 


Cuttings 


75 






1914 


) ) 


> > 


52 






1913 


> } 


Old plants 









1913 


} t 


(wounded) 


100 






1914 


Euphorbia 












variegata 


Seedlings 


6 


Potato E.P.C 


1912 


1913 


Beet 


) y 


50 






1913 


7> 


Plants 









1913 


Carnation 


Cuttings 


90 






1913 


J ) 


Young plants 






'See footnote, page 360. 



364 



Bulletin No. 189 



[Ju7ie, 



Table 11. — Concluded 



Strain 



Potato E.P.C. 
Potato E.P.I. 



Potato E.P.O.. 

Potato E. Sol. . 

Eadish 

Salvia 

Sedum 

Sugar cane . . 

Thistle 



"See footnote, page 360. 



Original 


Date of 






Per- 


date of 


inoculation 


Host 


Condition 


centage 


isolation 


experiment 






of loss" 


1912 


1913 


Eadish 


Seedlings 


15 


1912 


1913 


Carnation 


Cuttings 


65 




1913 


! > 


Young plants 


50 




1913 


> ) 


Old plants 







1913 


) > 


(wounded) 


100 




1913 


" 


Cuttings 


58 




1913 


) J 


Young plants 


43 




1913 


} > 


Old plants 







1913 


> } 


(wounded) 


50 




1913 


" 


Cuttings 


60 




1913 


" 


Old plants 







1913 


f > 


(wounded) 


100 




1913 


) ) 


Old plants 


75 




1913 


Beet 


Plants 







1913 


Eadish 


Seedlings 


1 




1913 


Turnii) 


} > 


99 


1912 


1913 


Carnation 


Cuttings 


2 




1914 


J J 


) } 


47 




1913 


} J 


Young plants 


33 




1914 


Salvia 










splendens 


Seedlings 


10 




1914 


!> 


Cuttings 


85 


1913 


1914 


Carnation 


} > 


100 




1914 


) ! 


Young plants 


20 


1912 


1914 


Amaranthui 










salicifoliuti 


Seedlings 







1913 


Carnation 


Cuttings 


90 




1914 


} ) 


} > 


24 




1913 


) ) 


Young plants 


13 




1913 


> ) 


Cuttings 


33 




1914 


' ' 


> ) 


47 




1913 


) ) 


Young plants 


14 




1913 


' ' 


Old plants 







19J3 


) ' 


(wounded' 


100 




1914 


Clover 


Seedlings 







1913 


Eggplant 


y ' 


5 




1913 


Lettuce 


)> 


60 




1914 


} > 


Plants 






GROWTH ON MEDIA 

In the course of these studies thirty-eight strains of Rhizoctonia 
were grown on five of the more common vegetable-extract agars and a 
solid synthetic medium. The composition of these media may be found 
in the appendix, together with a complete description of the growth 
of the various strains on them. 



1916] Parasitic Ehizoctonias in America 365 

As a rule the fungus isolated from carnation plants, when grown 
on green-bean agar, produced a rapid-growing mycelium, which was 
practically all aerial, loose, and tufted. The most characteristic fea- 
ture was the production of concentric zones, tho this was not invaria- 
ble. Of the many hundred cultures made during the past three years 
from diseased carnation plants on green-bean agar, 90 percent have 
shown this zonation. This characteristic was influenced by neither 
light nor temperature. A typical growth on this medium is shown in 
Fig. 20, ''Carnation R.H." A few of the carnation strains grown 
on the same medium and showing the same type of mycelium produced 
very indistinct zonation or none, as shown in Fig. 20, ' ' Carnation 
R.F." Zonation persisted to some extent when the carnation strains 
were grown on other media than green-bean agar, but it was not so 
characteristic. 

The two strains from potato did not grow so rapidly nor quite 
so luxuriantly on green-bean agar as did the carnation strains, but 
they produced the same even, tufted, zonate growth. Here the zones 
were closer together. (See Fig. 20, "Potato R. Sol.") 

The growth of the strain from corn on green-bean agar was similar 
to that of "Potato R. Sol." 

The growth on green-bean agar of the strains from eggplant, let- 
tuce, Chenopodium, and thistle was different from any of the other 
forms in that the mycelium grew along the surface, running out ra- 
dially in strands, which became larger and more tufted at the edge. 
(See Fig. 21, "Eggplant I.") 

The strains isolated from alternanthera, coleus, salvia, and poin- 
settia, when grown on green-bean agar, showed the same even, fluffy 
to tufted growth. This was also characteristic of the strains from 
cauliflower, cotton, and sugar cane. Zonation in these strains was 
varied. (See Fig. 21.) 

The strain from onion when grown on this agar differed radi- 
cally from the others. The mycelium was bright colored, finer, and 
almost all submerged. (See Fig. 20.) 

The other strains studied on green-bean agar cannot be put in 
definite groups, as they shade into one another. However, the growth 
of the mycelium was somewhat similar in each case; practically the 
only difference noted was in the extent of the zonation. 

On corn-meal agar the growth of the strains was similar to a large 
extent; the only great difference noted was in rapidity of growth. 
Zonation was very rare on this medium. 

The growth of the strains on oat agar was somewhat variable; 
zonation was sometimes present and sometimes absent. 

The most characteristic feature of the growth of the majority of 
the strains on potato agar was the turning brown of both the myce- 
lium and the medium. This same characteristic, but to a less degree, 



366 



Bulletin No. 18!) 



[Jime, 









Fig, 20. — Cultures of Rhizoctonia Strains Showing Development of Myce- 
lium ON Green-Bean Agar (Culture 48 Hours Old). Top Row: (1) Car- 
nation R.H. ; (2) Carnation R.F. Middle Row: (1) Potato R. Sol.; (2) 
Carrot. Bottom Row: (1) Cauliflower; (2) Onion 



' 



1D16] 



Parasitic Ehip^octonias in Ameri 



367 









SETTiA, (2) CoLKus I. BoTioM Row : (J) Egoplant I; (2) Lettoce 



368 



Bulletin No. 189 



[June, 




Fig. 22. — Cultures of Ehizoctonia Strains Showing Development of Sclero- 
TiA: (1) Alternanthera R.A.C; (2) Salvia; (3) Poinsettia; (4) Alter- 
nanthera R.A.F.; (5) Coleus; (6) Eggplant II; (7) Eggplant I; (8) 
Lettuce; (9) Chenopodium; (10) Thistle; (11) Carnation R.F.2; (12) 
Carnation E.S.; (13) Carnation R.2; (14) Carnation R.H.; (15) Carna- 
tion R.O.; (16) Aster; (17) Cotton I; (18) Beet; (19) Carrot; (20) 
Bean 



1916] 



Parasitic Rhizoctonias in America 



369 



I 




Sugar Cane; (H) -'^"*^^ Vi,^*rf»T,\Trn«TT« rarr4tus SM • (17) Dianthus 
ftvpsopHiLA- (15) Onion; (lb) Dianthus barbatus r^.ivi.. y'^'J „. 

?ZuMAR?usV (18) DIANTHUS SEQUERI; (19) DlANTHUS BARBATUS N.P. ; (20) 

Aster (carnation strain) 



370 Bulletin No. 189 [June, 

was found with the growth on potato-glucose agar. On both these 
media zonation was usually lacking or indistinct. 

On Agar XII most of the strains grew rather poorly and produced 
a white, flaky growth, with varying zonation. 

Early in the study of the characters of the strains on culture 
media, it was noticed that as there were characteristic differences in 
growth, so also were there differences in the production of sclerotia. 

The strains "Eggplant I," "Lettuce," "Chenopodium," and 
"Thistle" on green-bean agar all formed sclerotia in a characteristic 
manner. The sclerotia were white at first and flat, later turning black, 
and as the culture became older, curling up and becoming crust-like. 
All four of the forms mentioned above showed these same character- 
istics, alt ho they were originally obtained from widely separated locali- 
ties. (See Fig. 22.) The strain from onion produced sclerotia which 
were entirely different from those of other strains in that they were 
small (.5 to 1 millimeter in diamater), perfectly round, bright colored, 
and developed submerged in the medium. (See Fig. 23.) The strains 
"Buckwheat," "Carnation R.O.," " Gypsophila, " and "Sedum" 
rarely produced sclerotia in culture. Eepeated observations showed 
that this loss of power to produce sclerotia was the first sign of the de- 
generation and loss of virulence of the strain. 

All the other strains studied produced sclerotia which were at first 
white, later becoming brown. Altho the sclerotia from the strain from 
potato are similar to those from carnation when grown on culture 
media, on the potato tuber they are entirely different. For the most 
part the Rhizoctonia sclerotia on potato tubers which the writer has 
examined are flat and hard, have a black luster, and are in many re- 
spects like the sclerotia produced in culture media by the strains from 
eggplant, lettuce, etc. 

The only conclusion that can be drawn from this study of the 
growth of RJiizoctonia Solani on media is that the strains are very 
variable, those from the same host often producing a different growth, 
even^ on the same media, and that the differences in various cultural 
characters which are shown by strains from different hosts are no 
greater than dift'erences which may be manifested by two different 
strains isolated from the same host or by the same strain at different 
ages. 

MEASUREMENT OF MYCELIAL CELLS 

It was rather difficult to choose a standard in the measurement of 
the mycelial cells, because the cells varied in size at different ages and 
on different media. Finally the following standard was chosen: 
Hyphffi from the outer edge of a twenty-four hour old culture on 
green-bean agar were selected at random. The length and width of 
a cell from which the branch arose nearest the tip of the hypha, and 



1316] 



Parasitic Rhizoctonias in America 



371 



the distance on the inner side from the parent hj^pha to the first sep- 
tum of the branch, were measured. Ten cells of each strain were 
measured, and the averages of these measurements used for compari- 
son. 

As shown in Table 12, the measurements varied considerably, and 
this was true even with strains from the same host. In the three car- 
nation strains measured, the length of the mycelial cells varied from 
70^ to 181.7(11, a difference of 111.7/x. However, the average of ten 
measurements brings the difference down to some extent. A still more 
striking difference was noted in the strains from DiantJuis, where 
the smallest reading was 50/x and the largest 215/x, a difference of 165/a. 
Similar differences were also found in comparing the two other meas- 
urements. 

In all cases, altho the table does not bring out this point, different 
measurements of the cells of the various strains overlapped. For ex- 

Table 12. — Measurements op Mycelial Cells of Ehizoctonia 



Strain 



Alfalfa 

Alternanthera R.A.C. . . 
" E.A.F. . 

Amaranthus , 

Bean 

Beet 

Carnation R.H 

R.M.2 

" E.F.2 

Carrot 

Cauliflower 

Chenopodiinn 

Clover 

Coleus I 

Coleus II 

Corn 

Cotton I 

Dianthus barbatus S.M, 
N.P 

' ' sequeri 

' ' plumariiis. . . . 

Eggplant I 

II 

Gypsophila repens . . . . 

Lavatera 

Lettuce 

Poinsettia 

Salvia 

Sedum 

Sugar cane 

Sweet pea 

Thistle 



Length 


Width 


of cell 


of cell 


M 


w 


152.04 


5,76 


113.40 


3.92 


124.60 


4.94 


107.80 


4.83 


180.04 


6.57 


77.92 


4.34 


116.09 


4.59 


141.40 


5.60 


128.15 


5.19 


116.64 


4.42 


119.64 


4.20 


175.56 


5.43 


88.20 


5.32 


117.60 


5.04 


13.3.28 


4.97 


101.64 


4.39 


65.24 


5.50 


113.12 


5. ,58 


161.00 


5.27 


131.60 


6.29 


166.95 


5.65 


132.34 


4.20 


148.88 


5.60 


122.08 


3.55 


91.84 


5.89 


119.92 


4.39 


126.20 


3.44 


111.16 


5.01 


90.80 


4.48 


113.12 


4.09 


130.48 


5.04 


138.08 


4.62 



Distance from 

cell to septum 

of branch 



10.08 
6.72 
9.32 
7.98 

13.08 
6.52 

10.83 

10.49 

10.92 
9.60 
9.60 

11.20 
8.53 

10.21 

10.22 
9.24 

10.18 
9.44 

10.58 
6.44 

13.44 

11.65 
9.57 
8.03 
9.18 

10.54 
7.92 
9.93 
7.00 
6.57 
8.54 

11.48 



372 Bulletin No. 189 [June, 

ample, while the average length of a cell from "Cotton I" was only 
65)11, the largest reading was 127. 5/j,, which was higher than the small- 
est measurement of a cell of the strain ' ' Chenopodium, ' ' whose aver- 
age reading was 110;li higher than that of "Cotton I." If measure- 
ments are made of hyph^e forty-eight hours old, the differences are still 
more striking, even in the same strain. 

Hence, on the measurement of mycelial cells of RJiizoctonia Solani, 
as on the study of the growth on media, no conclusions can be based in 
regard to distinguishing the strains of this difficult species. 

SOIL SURVEY OF RHIZOCTONIA 

As shown in Table 1, RJiizoctonia Solani has been observed in al- 
most every state in the Union, and causes injury to a large number of 
plants under various conditions and in widely different types of soils. 
To determine to how great an extent Rhizoctonia is actually present 
in the soil, several surveys were made at the University of Illinois in 
fields containing a variety of plants. 

Survey of the Perennial Garden, Horticultural Grounds, April 28 
to May 1, 1914. — During the summer and fall of 1913, Rhizoctonia 
was isolated from a number of perennial plants in the garden. To 
determine whether the fungus lived on the dead parts of the plants 
or in the soil or both during the winter season, a survey was made the 
following spring. 

Since it is somewhat difficult to isolate Rhizoctonia direexly from 
the soil by means of soil cultures, the following method was devised 
to determine its presence in the soil: Small patches of ground were 
selected over the field about twenty feet apart, so that the results might 
give a fair idea of the distribution of the fungus. Each space was 
cleared except for a small living plant, and the soil thoroly watered. 
Three sheets of moistened filter paper were then placed on the 
ground over the plant. To prevent evaporation, a small flat with a 
layer of wet moss attached to the bottom was placed over the paper. 
The flats had previously been sterilized in formalin (1-100) and the 
moss sterilized in the autoclave. Thru several small holes in the bot- 
tom of the flat, water was added to the moss from day to day to keep 
it moist. At the end of the fifth day the plant parts were removed 
to the laboratory. 

The presence of the fungus was determined by means of pure cul- 
tures and by microscopic observation. Where the identification de- 
pended solely on microscopic observations, the material was left in a 
covered dish for several days until the strands of the fungus became 
older, when they could be distinguished more readily by their color. 

In thirteen cases out of sixteen Rhizoctonia was found present on 
the dead or living pieces of plants placed in contact with the soil; 



1916] 



Parasitic Rhizoctonias in America 



373 



+- 


4- 


+ 


■»- 


+■ 


+ 


+- 
f 


4- 


< 


1 


Ol 


CL 


i::' 


:<: 


jc: 


^ 


n 


ti.' 


L. 


r 


z 


r 


2 


Q.- 


tL' 


z 


2 


lO 


x 


^ 


J 


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374 Bulletin No. 189 . [Jime, 

hence we may conclude that this fungus was very abundant both in the 
soil and on the plant parts in contact with the soil. 

Survey of Plot Used for Field l7ioculatio7i Experiments, May 6 
to May 11, 1914. — This plot, formerly used by the Agronomy Depart- 
ment, had been under cultivation for a number of years. The pre- 
vious season the field had been in potatoes and corn. The old potato 
stalks were left scattered over the field during the winter. 

A survey of the plot was made before plowing, following the same 
method as was used as in the preceding experiment. Sixteen flats 
were set out twenty-five feet apart. After five days an examination for 
the presence of Rhizoctonia was made. By microscopic examination 
and pure cultures, Rhizoctonia was detected in ten trials out of sixteen 
on this plot. 

Survey of Agronomy Plots on North Farm, September 26 to Octo- 
ber 2, 1914. — Here a more extensive survey was conducted. The 
agronomy plots on the North Farm were chosen for this purpose be- 
cause of the fact that they had been under continuous cultivation 
since 1895, and showed the effects of different methods of soil treat- 
ment, various systems of crop rotation, and the application of differ- 
ent kinds of food. (For treatments and rotations used, see Fig. 24.) 
These plots are also typical of the prairie soil, which represents the 
most extensive and important type of soil in Illinois. 

The procedure followed in this survey was modified as follows: 
Instead of a flat, a seven-inch flower pot, which could be easily steri- 
lized and dried, was employed. Small cheesecloth bags were filled with 
sphagnum moss ; these were sterilized in the autoclave. When ready 
for use, the bags were moistened and placed in the bottom of the pots 
and secured in such a way that they remained in position when the 
pots were inverted. A small patch of soil, one in each plat, was lev- 
eled off, only a small living plant or some plant debris being left. 
Several thicknesses of moistened filter paper were then laid over the 
spot, and a flower pot was placed over the whole. The pot was pushed 
into the ground about three inches and the soil heaped up around it 
on the outside. The pots were left in this condition about one week, 
during which time the moss was moistened at intervals. Conditions 
were very favorable to the growth of Rhizoctonia if it was present 
in the soil. When the pots were lifted, the plant parts or debris with 
some of the soil were wrapped in the filter paper and placed under 
bell jars. The contents of the papers were then examined for the 
presence of Rhizoctonia. 

These plots showing the effects of diverse treatments yielded R. 
Solani in sixty-four trials out of seventy. The six negative results 
were scattered over the field, so that no correlation between the treat- 
ment of the plot and the presence of Rhizoctonia can be said to exist. 



1916] Parasitic Bhizoctonias in America 375 

The results of these experiments admit of no question as to the 
presence of the fungus RJiizoctonia Solani in the soil in the vicinity 
of Urbana. 

PARASITISM OF RHIZOCTONIA SOLANI KUHN 

That R. Solani is an active parasite under certain conditions would 
never be questioned by anyone who had seen a severe attack of car- 
nation stem rot in the field or greenhouse. In the cutting bench 
this fungus causes damping-off of cuttings in an incredibly short time, 
while seedlings damp oft' almost as fast. At times Rhizoetonia causes 
considerable loss in potato fields. In fact, it may become epidemic 
and cause serious injury to most of the field, vegetable, and floricul- 
tural crops. 

The epidemics are apparently' due to a combination of factors, 
such as the presence of a virulent strain of the fungus, a susceptible 
variety of plant, and optimum conditions of temperature and moisture 
for infection and development. Under ordinary conditions most of 
the strains appear to be weak parasites. 

The apparently universal presence of Rhizoetonia in the soil, 
where it can live indefinitely on dead organic matter under ordinary 
conditions, makes it a dangerous fungus. The fact that it shows no 
marked specialization and can attack a large variety of weeds assists 
in harboring the fungus and in keeping up its virulence. The sclero- 
tJa and mycelium can live under adverse conditions for several years. 
Transfers from soil cultures started in December, 1911, kept in the 
laljoratory, and allowed to dry out, yielded pure cultures as late as 
July, 1914. Soil cultures left in the field during the entire winter 
yielded the fungus in the spring. 

In all but one of the experiments inoculation was brought about 
without wounding the plants in any way, in many cases the fungus 
being simply mixed with the soil in which the plants were growing. 
The results furnish convincing proof of the parasitism of the fungus. 
The conditions under which all strains manifested their greatest para- 
sitism were primarily a high temperature (above 88° F.) and a soil 
moisture content either too low or too high for the best development of 
the plant. When carnation plants growing in soil inoculated with 
Rhizoetonia were given a heavy watering and the soil was then allowed 
to dry out, they were killed more rapidly than plants growing under 
the same conditions but in continually over-watered soil. Plants 
watered normally died off slowly and the percentage of loss was very 
much less. 

Repeated observations in greenhouse and field have shown that a 
certain amount of the mycelium must be present before the fungus is 
able to attack and kill the plant. A small amount of mycelium has 
always been observed around a carnation plant in the bench a week 



376 Bulletin No. 189 [June, 

or more before the plant showed any signs of being diseased. In fact, 
a certain amount of mycelium is always present in the carnation soil 
in the greenhouse, but it is only when the temperature is high that 
the fungus is able to attack the plants. This explains why stem rot 
of carnations is more severe during the summer months than in the 
winter. (See Experiment 6, page 349.) In the field similar conditions 
ai'e necessary to result in infection of a plant. 

Investigations to determine how much vigor the mycelium must 
attain before the fungus can attack a plant are now in progress, as 
is also a histological and enzymatic study. 

SUMMARY 

1. At the present time there are recognized in America two 
species of truly parasitic Rhizoctonias : The common form, RJiizoctonia 
Solani Kiihn {Corticium vagum B. & C), widely distributed and oc- 
curring on a great number of hosts; and R. Crocorum (Pers.) DC, 
with a limited distribution on alfalfa and potato tubers. A third 
Rhizoctonia, Corticium ocliraleucum (Noack) Burt, is found on the 
leaves of pomaceous fruit trees, while a fourth species isolated from 
damped-off onion seedlings is of questionable parasitism. 

2. The plants thus far listed as more or less subject to attacks of 
RJiizoctonia Solani Kiihn in the United States number about 165 
species. All the more important families of dicotyledons are included 
in this list, as well as a number of monocotyledons, several gymno- 
sperms, and Equisetum. Most of the fioricultural plants, vegetable 
and field crops, herbaceous plants, and many weeds are susceptible to 
attacks of this fungus. 

3. The symptoms produced by RJiizoctonia Solani Kiihn in nat- 
ural infection are largely similar when appearing on the same type 
of host. The damping-off of seedlings and cuttings of various plants 
is identical, as is the rotting of a number of root crops. In most her- 
baceous plants a stem rot is produced, the symptoms of which are also 
identical on the various hosts. On very resistant plants lesions only 
are formed ; these are apparently the same on the different hosts. 

4. From these inoculation experiments with a large number of 
different types of plants, we must conclude that all the strains studied, 
which were obtained from a wide range of hosts of diverse geographi- 
cal origin, can attack the same species of plant and produce the same 
characteristic symptoms. No marked specialization was noted in any of 
the strains. Thus all the strains studied can be included under one 
form, RJiizoctonia Solani Kiihn. The inoculation experiments show 
further that the virulence of R. SoUmi is very variable, as is also the 
degree of resistance of the various host plants, both depending on a 
number of varying factors. 



I 'J 16] Parasitic Ehizoctonias in America 377 

5. Studies of the growth of Rliizoctonia Solani Kiihn on media 
show that the strains are very variable, those from the same host 
often producing a different growth even on the same media, and that 
the differences in various cultural characters which are shown by 
strains from unlike hosts are no greater than the differences which 
may be manifested by two different strains isolated from the same host 
or by the same strain at different ages. 

6. Measurements of mycelial cells of BJiizoctonia Solani Kiihn 
showed such large variations, not only between strains from different 
hosts but also between different strains from the same host, that no 
standard could be determined on for distinguishing the different 
strains. 

7. By means of a local soil survey, it was found that Rliizoctonia 
Solani Kiihn is abundant in cultivated land, where it may live either 
on dead organic matter in the soil or on weeds and other plants. 

8. A certain vigor of mycelium must be attained before Rliizoc- 
tonia Solani Kiihn is able to attack a plant. A high temperature 
(88° P.), together with either too little or too much moisture, deter- 
mines to a large degree the virulence of the strains. It is only under 
certain conditions that the fungus becomes a dangerous parasite. 



The writer gratefully acknowledges his indebtedness to Dr. F. L. 
Stevens, Professor of Plant Patholog>% and to Dr. J. T. Barrett, for- 
mer Chief Assistant in Botany, for their kind assistance and encour- 
agement. He wishes also to thank Professor H. B. Dorner, Assistant 
Chief in Floriculture ; Mr. C. C. Rees, formerly Assistant in Floricul- 
tural Pathology ; and other members of the Division of Floriculture 
for assistance rendered during the progress of this work. 



378 Bulletin No. 189 [June, 

APPENDIX 

COMPOSITION OF MEDIA USED IN EXPERIMENTS 

Corn-Meal Agar (Shear''). — To 4 teaspoonfuls of corn meal add 1 liter of dis- 
tilled water. Reap in water bath for one hour at a temperature below 60 °C. 
Strain thru gauze, and to the filtrate add 1 percent agar flour. Steam three-quarters 
of an hour. Filter thru paper tube and place in autoclave for 15 minutes at 
115° C. 

Grecii-Bean Agar. — ,300 grams young string beans cooked in 500 ee wat»3r 
for one hour and sti"ained thru cloth. 15 grams agar (powdered) melted in 500 cc. 
water. Mix the two, add enough water to make 1000 cc, add 6 to 8 grams egg 
albumen, and boil in autoclave. Filter thru cotton. 

Oat Agar (Clinton^). — 200 grams oats ground fine thru a coffee mill and 
soaked in 500 cc. water for one hour. 15 grams agar melted in 500 cc. water and 
strained thru cheesecloth. Mix the two but do not filter, since the most nutrient 
part of the medium would he lost. 

Potato Agar. — 300 grams peeled potatoes, sliced as thin as possible and cooked 
in 500 cc. Avater for one hour. Strain thru cloth. 15 grams agar (powdered) 
melted in 500 cc. water. Mix the two and add enough water to make 1000 cc. 
Add 6 to 8 grams egg albumen (powdered) and boil in autoclave for a short time. 
Filter thru cotton. 

Potato-Glucose Agar. — 290 grams peeled potatoes, sliced as thin as possible 
and cooked in 500 cc. water for one hour. Strain thru cloth and add 20 grams of 
glucose. 15 grams agar (powdered) melted in 500 cc. water. Mix the two, add 
enough water to make 1000 cc, add 6 to 8 grams egg albumen (powdorod), ajid 
boil in autoclave for short time. Filter thru cotton. 

Agar (Cook") 

Water 1000.00 cc 

Agar 15.00 gra 

Glucose 20.00 

Ammonium nitrate 1.00 

Potassium nitrate 1.00 

Ammonium sulfate 1.00 

Magnesium sulfate .25 

Dipotassium phosphate .25 

Calcium chlorid'' .01 

GROWTH ON MEDIA 

* * Alfalfa ' ' 

On Corn-Meal Agar. — Growth poor aiul rather slow. Mycelium white, fine, 
submerged, and scav^ely visible. No coloring of the medium. No zonation. 

On Green-Bean Agar. — Growth poor and slow. Mycelium white, fine, loose, 
and becoming somewhat tufted. Zonation. Like strain from corn. 

On Potato Agar. — Growth rather slow. Characterized by the dark color 
of the mycelium and the turning of the medium to a darker color. Hypha) loose, 
fine, and practically all submerged. No zonation. 

"U. S. Dept. Agr., Bur. Plant Indus., Bui. 252, 15. 1913. 
"Conn. Sta. Rpt. (1909-10), 32, 760. 1911. 
•'Del. Sta. Bui. 91, 12. 1911. 
''Omitted from formula used. 



1916] Parasitic Ehizoctonias in America 379 

Stewnrt/-'' in reporting the damping-off of alfalfa seedlings in the greenhoiiso 
and the crown lot of mature plants in the field, states that "the one causing 
danipinff-off of seedlings in the greenhouse is different from the one found in the 
tield. WTien grown on potato agar (slightly acid, neutral, or slightly alkaline), 
the former produces a conspicuous dark brown discoloration of the medium, whereas 
the latter discolors it only slightly. This character may b'^ useful in the identi- 
fication of the damping-off Ehizoctonia. Such discoloration of the medium is not 
common among the species of Rhizoctonia. " It is interesting to note that the 
strain obtained from Louisiana causing a damping-off of alfalfa seedlings and a 
number of other strains showed the same discoloration as the one studied by 
Stewart. 

On Aqnr XII. — Growth fair. Few loose, erect hyphse, becoming denser and 
finally forming an indistinct zone. 

"Alternanthera R. a. C. " 

On Corn-Mcol Agar. — Growth very rapid, but not dense. Mycelium white, 
loose, aerial, and fine. No zonation. 

On Green-Bean Agar. — Growth good. Mycelium tufted and compact, not 
turning darker. Zonation somewhat distinct at end of third day. Three zones 
present. 

On Oat Aoor. — Growth rapid. Mycelium flat, and very compact, forming a 
mat over the surface. Zonation. 

Oil Fotoio Agar. — Growth very rapid, with zone formation beginning im- 
mediately. Mycelium all aerial and growing very compactly. Plate (vns covered 
at end of forty-eight hours and showed two distinct zones and one indistinct. 

0)1 Potato-GJvcose Agar. — Growth rapid; plate covered in forty-eight hours. 
Mycelium white, loose, and flaky. Zonation. 

On Agar A77.-— Growth good. Mycelium white, fine, compact, and somewhat 
flaky. Zon;ition. 

. " Alternanthera R. a. F." 

On the various media this strain produced the same kind of growth in each 
case as the strain from the cutting bench, except that it grew more rapidly. 

' * Aster ' ' 

On Green-Bean Agar. — Growth fair. Mycelium white, loose, regular, iind fiat, 
becoming somewhat tufted. Four zones formed at end of the fourth day. 

On Oat Agar. — Growth fair. Mycelium white, loose, flat, and regular, be- 
coming fluffy and. tufted. Like strain ' ' Carnation R. F. " Five zones at end of 
fourth day. 

On Potato-Glucose Agar.— Growth slow and poor. Mycelium mostly submerged 
and turning brown. No zonation. 

On Agar XII. — Growth fair. Mycelium white, loose, flat, and regular, be- 
coming somewhat tufted. Zonation. 

"Bean" 

On Corn-Meal Agar. — Growth very poor; scarcely visible. Mycelium white, 
fine, somewhat aeiial. No zonation. 

071 Green-Bean Agar. — Growth slow. Mycelium fine, aerial, loose, and white, 
darkening with age. Two zones formed, but not very distinct; otherwise like the 
strain from carrot. 

On Potato Agar. — Growth fair. Mycelium fine, more or less submerged, and 
discoloring the medium only slightly. No zonation. 



380 Bulletin No. 189 [June, 

On Agar XII. — Growth rapid. Mycelium somewhat tufted and dense. Three 
distinct zones present. 

' ' Beet ' ' 

On Green-Bean Agar. — Growth good. Mycelium flat and compact. Several 
zones present. 

' ' Begonia ' ' 

On Corn-Meol Agar. — Growth fair. Mycelium rather compact and white. No 
zonation. 

On Green-Bean Agar. — Growth fair. Mycelium white, tufted, and compact. 
Zonation indistinct. 

On Potato Agar. — Growth fair. Mycelium compact, dense, and white; me- 
dium turning dark. Zonation. 

On Agar XII. — Growth scant. Mycelium white, fine, and loose. No zonation. 

' ' Carnation K. K. " 

On Corn-Meal Agar.—Growih good. Mycelium white, making a rather dense 
growth for corn-moal agar. Zonation indistinct. 

On Green-Bean Agar. — Growth good. Like strain "Carnation E. H. " 

On Oat Agar- — Growth good. Mycelium white, loose, edge tufteil. Zonation. 

On Potato Agar. — Growth poor. Mycelium loo:e and scattering, medir.m turn- 
ing darker. Zonation indistinct. 

On Agar XII. — Growth poor. Mycelium white, loose, and scattered; edge 
irregular. Zonation indistinct. 

"Carnation E. H." 

On (Jorn-Meal Agar. — Growth fair. Mycelium white, fine, and in loose strands; 
rather dense at center. No zonation. 

On Green-Bean Agar. — Growth good. Mycelium dark at center, loose, and 
tufted ; edge irregular. Zonation very characteristic of the strains isolated from 
diseased carnation plants. 

On Potato Agar. — Growth poor. Mycelium fine and scattered; edge irregular. 
Mycelium causing a characteristic browning of the medium. Zonation indistinct. 

On Agar XII. — Growth poor. Mycelium white, fine, loose, and scattered. No 
zonation. 

"Carnation E. S, " 

On Corn-Meal Agar. — Growth fair. Mycelium white, fine, but rather dense at 
center; edge regular. Zonation. 

On Green-Bean Agar. — Growth good. Mycelium loose, white, and tufted; edge 
regular. Later, mycelium turned brown. Zonation somewhat indistinct. 

On Potato Agar. — Growth poor and scant. Mycelium producing a distinct 
browning of the agar. Zones indistinct. 

On Agar XII. — Growth poor. Mycelium white, scant, loose, and flat. Zonation. 

' ' Carnation E. F. " 

On Corn-Meal Agar. — Growth good. Mycelium white, loose, and somewhat 
tufted. No zonation. 

On Green-Bean Agar.- — Growth fair. Mycelium white, compact, and tufted. 
Zonation somev/hat indistinct. 



1916] Parasitic Ehizoctonias in America 381 

On Oat Agar. — Growth good. Mycelium white, loose, flat, and fairly dense; 
edge tufted. Zonal ion. 

On Potato Agar. — Growth poor. Mycelium scant, like that produced by strains 
from carnation. 

On Potato-Glucose Agar. — Growth poor. Mycelium white, loose, scattered, 
and somewhat flai^y ; edge very irregular. Zonation. 

Oih Agar XII. — Growth poor. Mycelium white, tine, loose, flat, and scatter- 
ing; edge very irregulai. Zonation indistinct. 

"Carnation E.M.2" 

On Corn-Meal Agar. — Growth good. Mycelium white, tufted, and somewhat 
compact. No zonation. 

On Green-Bean Agar. — Growth fair. Mycelium white, tufted, ard compact. 
Zonation indistinct. 

On Oat Agar. — Growth fair. Mycelium white, loose, and somewhat flaky at 
center; edge loose and irregular. Zonation. 

0)1 Potato Agar. — Growth poor. Mycelium loose and fine. Zonation indis- 
tinct. 

On PoioJo-GTneose Agar. — Growth fair. Mycelium brown, loose, and flat; 
edge loose and tufted. No zonation. 

On Agar XII. — Growth fair. Mycelium white, loose, flat, and scattered. No 
zonation. 

"Carnation E.D.C." 

On Corn-Meal Agar. — Growth good. Mycelium white, loose, tufted, and rather 
dense. No zonation. 

On Green-JSean Agar. — Growth good. Mycelium white, loose, tufted, and 
dense. Zonation distinct. 

On Oat Agar. — Growth fair. Mycelium white, somewhat dense at center, and 
more tufted at edge. Zonation. 

On Potato Agar. — Growth poor. Mycelium loose and flat, darkening slowly 
with age. Zoi.ation indistinct. 

On Potato-Glucose Agar. — Growth fair. Mycelium white, flat, and flaky at 
center; edge loose and fluffy. Zones numerous and distinct. 

On Agar XII. — Growth poor. Mycelium white, somewhat flaky at center; edge 
irregular and scattered. Zonation. 

' ' Carrot ' ' 

On Corn-Meal Agar. — Growth good. Mycelium white, fine, and somewhat com- 
pact. No zonation. 

On Green-Bean Agar. — Growth poor. Mycelium loose, flat, and somewhat 
fluffy; white at first, followed by purplish tinge. Zonation not very distinct. 

On Oat Agar. — Growth fair. Mycelium white, fine, loose, and flat. Zonation 
indistinct. 

On Potato Agar. — Growth fair. Mycelium dark, dense, and compact. Zona- 
tion indistinct. 

On Poiato-Glucosc Agar. — Growth fair. Mycelium dark, loose, flat, and flaky. 
Four to six zones present. 

On Agar XII. — Growth slow. Mycelium white, loose, and somewhat flaky. 
Zonation. 



382 Bulletin No. 189 [June, 

' ' Cauliflower ' ' 

On CornMcfll Agar. — Growth poor. Mycelium white, loose, and scant. No 
zonalion. 

On Green-Bean Agar. — Growth good. Mycelium white, tufted, and compact; 
edge regular. Zonation. 

On Oat Agar. — Growth good. Mycelium white, fine, loose, flat, and dense, 
running out in characteristic strands. No zonation. 

On Fotato-Glucose Agar. — Growth fair. Mycelium dark, loose, flat, and flaky. 
One zone at outer edge. 

On Agar XII. — Growth good. Mycelium white, loose, flat, and flaky. Zonation. 

' ' Chenopodium ' ' 

On Grecn-Bcan Agar. — Growth good. Mycelium white, flat, radial, and com- 
pact. No zonation. 

"Clover (Red) " 
On Green-Bean Agar. — Growth good. Mycelium flat and compact. Zonation. 

"COLEUS I" 

On Corn-Meal Agar. — Growth good. Mycelium white, loose, and somewhat 
compact. No zonalion. 

On Green-Bean Agar.- — Growth good. Mycelium white, tufted, and compact, 
Zonation indistinct. 

On Oat Agar. — Growth good. Mycelium white, loose, and flat ; edge fluffy. 
No zonation. 

On Potato Agar.- — Growth fair. Mycelium loose and tufted, turning darker 
with age. No zonation. 

On Potato-Glucose Agar.- — Growth fai>. Mycelium dark, loose, and flaky; 
edge irregular. Zonation. 

On Agar XII. — GroAvth good. Mycelium loose, dense, and white. No zonation. 

' ' Corn ' ' 

On Corn-Meal Agar. — Growth poor. Mycelium white, fine, and scattered. No 
zonation. 

On Green-Bean Agar. — Growth fair. Mycelium loose at edge and somewhat 
compact, turning darker with purplish tinge. Two distinct zones. 

On Potato Agar, — Growth fair. Mycelium dense and compact. Mycelium and 
medium turned dark. Zonation indistinct. 

On Agar XII. — Growth fair. Mycelium white, loose, tufted, and rather dense 
at center. Zonation, 

"Cotton I" 

On Green-Bean Agar. — Growth fair. Mycelium loose, tufted, dense, and white. 
Two zones present. 

On Oat Agar. — Growth good. Mycelium white, loose, flat, dense, and radial, 
later taking on a wrinkled appearance. No zonation. 

On Potato-Glucose Agar. — Growth fair. Mycelium white, flat, dense, flaky, 
and regular; loose at edge. Zonation indistinct. 



1916] Parasitic Rhizoctonias in America 383 

On Agar XII. — Growth fair. Mycelium flat, somewhat dense, flak}', and 
white at center; edge loose. Two distinct zones. 

"Cotton II" 

On Green-Bean Agar. — Growth fair. Mycelium loose, tufted, and fairly dense, 
later turning brown. Two zones present. 

071 Oat Agar. — Growth fair. Mycelium white, fine, loose, and flat, forming a 
mat over surface of the medium. One zone present. 

On Potato-Glucose Agar. — Growth fair. Mycelium loose, flat, and fairly dense; 
edge irregular. Later both mycelium and medium turned brown. Two zones 
present. 

On Agar XII. — Growth fair. Mycelium white, loose, and somewhat tufted. 
Three zones present. 

"DiANTHUS BARBATUS N.P. " 

On Green-Bean Agar. — Growth fair. Mycelium tufted and compact. Zonation 
indistinct. 

"DiANTHUS BARBATUS S.M. " 

On Green-Bean Agar. — Growth good. Mycelium tufted and compact. Zona- 
tion rather indistinct. . 

' ' DiANTHUS PLUMARIUS ' ' 

On Green-Bean Agar. — Growth good. Mycelium loose, white, and somewhat 
tufted ; edge regular. Zonation characteristic of the carnation strains. 

' ' DiANTHUS SEQUERI ' ' 

On Green-Bean Agar. — Growth good. Mycelium loose, white, and sonieuiiac 
fluffy; edge regular. Zonation characteristic of carnation strains in all respects. 

" Eggplant I" 

On Corn-Meal Agar. — Growth poor. Mycelium white, fine, and mostly sub- 
merged. No zonation. 

On Green-Bean Agar. — Growth good. Mycelium white, flat, radial, compact, 
and dense. One zone at center. 

On Oat Agar. — Growth fair. Mycelium white, loose, flat, interwoven, and 
somewhat tufted. Zonation. 

On Potato Agar. — Growth good. Mycelium dark, compact, dense, and radial. 
No zonation. 

On Potato-Glucose Agar. — Growth fair. Mycelium in radial strands, flat, and 
white. No zonation. 

On Agar XII. — Growth fair. Mycelium white, flat, dense, and compact. 
One zone present. 

' ' Gypsophila ' ' 

On Green-Bean Agar. — Growth fair. Mycelium white, fluffy, and somewhat 
compact. Zonation very characteristic of strains from carnation. 

. * ' Lavatera ' ' 

On Green-Bean Agar. — Growth good. Mycelium white, loose, and tufted; edge 
even. Several zones present. 



384 Bulletin No. 189 [June, 

' ' Lettuce ' ' 

On Corn-Meal Agar. — Growth fair. Mycelium white, fine, slightly aerial, ard 
somewhat flaky. No zonation. 

On Green-Bean Agar. — Growth good. Mycelium white, loose, flat, and rather 
dense, running out in strands. One indistinct zone present. 

On Oat Agar. — Growth fair. Mycelium white, loose, flat, interwoven, and 
somewhat tufted. One zone present. 

On Potato Agar. — Growth fair. Mycelium dark, fine, and practically all sub- 
merged. No zonation. 

On Potato-Glucose Agar.- — Growth good. Mycelium white and flat, running 
out in radial strands. No zonation. 

On Agar XII. — Growth good. Mycelium white, loose, flat, and rather dense. 
No zonation. 

' ' Onion ' ' 

On Green-Bean Agar. — Growth fair. Bright colored mycelium, fine and sub- 
merged at center; a little aerial mycelium at the outer edge, where it was some- 
what loose. No zonation. 

On Potato Agar. — Growth fair. Mycelium fine, scarcely visible, and of a 
bright color. No zonation. 

On Agar XII. — Growth fair. No aerial mycelium. No zonation. 

' ' POINSETTIA ' ' 

On Corn-Meal Agar.- — Growth fair. Mycelium white, dense, fluffy, and com- 
pact. Zonation indistinct. 

On Green-Bean Agar. — Growth fair. Mycelium white, loose, compact, and 
fluffy. No zonation. 

On, Oat Agar. — Growth good. Mycelium white, loose, flat, and radial; edge 
somewhat fluffy. No zonation. 

On Potato Agar. — Growth fair. Mycelium somewhat flaky and compact. Three, 
zones present. 

On Potato-Glucose Agar. — Growth fair. Mycelium brown and flat at center; 
outer edge white, loose, and somewhat flaky. Zonation indistinct. 

On Agar XII. — Growth fair. Mycelium white, flat, dense, and radial, like 
alternanthera. One zone. 

"Potato E. Sol." 
On Corn-Meal Agar. — Growth fair. Mycelium fine and flat. No zonation. 

On Green-Bean Agar. — Growth fair. Mycelium loose at edge, compact and 
fluffy at center. Several zones present, two distinct. 

On Potato ^fifrtr.— Growth fair. Mycelium white and fluffy. One zone at center. 

On Agar XII. — Growth jioor. Mycelium mostly submerged and somewhat com- 
pact; flaky at center. Zonation. 

' ' Potato E.P.O. ' ' 

On Corn-Meal Agar. — Growth fair. Mycelium white, fine, and rather scant. 
No zonation. 

On Green-Bean Agar. — Growth good. Mycelium loose at edge, flat, dense, 
somewhat fluffy, and rather dark. Three zones present. Growth very much like 
strains from carnation. 



1916] Parasitic Ehizoctonias in America 385 

On Potato Agar. — Growth fair. Mycelium dark, loose, and fluffy. Zonation 
distinct. 

On Potato-Glucose Agar. — Growth fair. Mycelium white, flat, loose at edge, 
and flaky at center. Three zones present. 

On Agar XII. — Growth very slow. Mycelium white, dense, and bushy, form- 
ing a tuft at the center. No zonation. 

' ' Salvia ' ' 

On Green-Bean Agar. — Growth good. Mycelium white, tufted, and compact. 
Zonation indistinct. 

On Oat Agar. — Growth good. Mycelium white, loose, flat, rather dense, and 
radial. Zonation indistinct. 

On Potato-Glucose Agar. — Growth fair. Mycelium white and flaky at center; 
edge loose and tufted. Zonation indistinct. 

On Agar XII. — Growth good. Mycelium white and flaky at center; edge loose 
and tufted. Zonation indistinct. 

' ' Sedum ' ' 

On Green-Bean Agar. — Growth good. Mycelium flat and compact. One zone 
present. 

' ' Sugar Cane ' ' 

On Corn-Meal Agar. — Growth fair. Mycelium white, fine, and scarcely visi- 
ble. No zonation. 

On Green-Bean Agar.- — Growth fair. Mycelium white, loose, and tufted. Zones 
present. 

On Potato Agar. — Growth fair. Mycelium white, fine, and practically all sub- 
merged. Two indistinct zones present. 

On Agar XII. — Growth fair. Mycelium white, fine, and running out in strands 
from the center. No zonation. 

' ' Sweet Pea ' ' 

On Green-Bean Agar. — Growth good. Mycelium flat and compact. One zone 
present. In many respects like strain from carnation. 

"Thistle" 

On Corn-Meal Agar. — Growth fair. Mycelium white, running out in strands; 
flat at center, and somewhat loose at edge. No zonation. 

On Green-Bean Agar.- — G^-owth good. Mycelium white, flat, radial, and com- 
pact at center; edge somewhat loose and fluffy. Zonation indistinct. 

On Oat Agar. — Growth good. Mycelium white, flat, dense, and radial. No 
zonation. 

On Potato Agar. — Growth fair. Mycelium white, flat, and somewhat compact, 
running out in strands. No zonation. 

On Potato-Glucose Agar. — Growth fair. Characterized by a white, radial, flat 
mycelium. No zonation. 

On Agar XII. — Growth fair. Mycelium, white, flat, compact, and flaky at cen- 
ter, becoming looser at edge. No zonation. 



386 Bulletin Ko. 189 [June, 



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BIOGRAPHICAL SKETCH 

George Leo Peltier was born in Merrill, Wisconsin, on INIay 8, 1888. 
He secured his early education in the public schools of Merrill and 
Grand Rapids. He then entered the LTniversity of Wisconsin and in 
June, 1910, received the degree of bachelor of arts from that institu- 
tion. The following year he spent as a science teacher in the high 
school at Wauwatosa, Wisconsin. During the year 1911-12 he held the 
position of Teaching Fellow in the Shaw School of Botany (Missouri 
Botanical Garden), and in June received the degree of master of arts 
fi'om Washington LTniversity. Since that time he has held the position 
of Assistant in Floricultural Pathology in the Agricultural Experi- 
ment Station of the University of Illinois. 

Dr. Peltier is a member of Sigma Xi, Gamma Alpha, and the Amer- 
ican Phytopathological Society. 

Publications 

A Consideration of the Physiology and Life History of a Parasitic 
Botrytis on Pepper and Lettuce. Mo. Bot. Gard. Rpt.. 23, 41- 
74, 5 pis. 1912. 

Carnation Diseases. Florists' Exchange. 33, 5. 252-253, 1 pi.; 6, 
320; 7, 372, 3 pis. 1914. 

Rhizoctonia in Amei'ica. Abs. in Phytopath., 4, 40(5. 1914. 



